Wrapping a whirlwind day of campaigning, President Barack Obama joined Bill Clinton — the last Democratic president, and vocal advocate for Obama — at a massive rally Saturday evening in northern Virginia. 

Before a crowd estimated at 24,000, Obama both literally and figuratively embraced Clinton, who has emerged as one of the most dogged advocates for the president's re-election campaign this fall. 

"He has been traveling all across the country for this campaign. He's been laying out the stakes so well that our team basically calls him the 'Secretary of Explaining Stuff,'" Obama said. "He was a great president; he has been a great friend."

As the final weekend of the 2012 campaign raised the question of which candidate, Obama or Republican presidential nominee Mitt Romney, would best move Washington past its intractable problems, Clinton, a president who has only grown more popular since leaving office, offered Obama his imprimatur. 

"As you see, I have given my voice in the service of my president," the hoarse former president said, following some local favorites, the Dave Matthews Band, at the rally in suburban Washington. 

NBC Politics coverage of the 2012 campaign:

• Uncertain finale looms amid weekend campaign blitz
• Romney implores Colorado for 'one last push'
• Biden zings Romney in Colorado
• Ryan travels to Pennsylvania, trying to put state in play
• Obama plays up 'trust' in battleground Ohio
• Obama aide explains 'voting is best revenge' comment
• Ryan: 'We believe in change and hope'
• Romney strikes optimistic tone as final weekend opens
• Polls: Obama stays ahead in Ohio, deadlocked with Romney in Fla.
• GOP's chances at Senate imperiled by self-inflicted wounds

Both Obama and Romney spent the day criss-crossing the United States to make a firmly centrist appeal, each of them trying to sound upbeat as the clock counts down on Election 2012. Each candidate drew thousands — sometimes tens of thousands — of supporters to rallies in Iowa, Wisconsin, Colorado, Iowa, Virginia, Ohio and beyond. And each candidate argued he was the one who could break through the gridlock in a Congress beset for the past two years by bitter partisan fights.

"You know that if the president is re-elected, he'll still be unable to work with the people in Congress," Romney told a sprawling crowd in Colorado. "He's ignored them. He's blamed them. He's attacked them."

Romney spent much of the campaign's final weekend arguing he was the candidate of "change," co-opting Obama's 2008 message to use four years later against the president. 

Whether the Republican candidate's claim to to the mantle of change would resonate with a handful of remaining swing voters in just a few battleground states was unclear. Obama seemed to enjoy an edge in states like Iowa, leading Romney by five points among likely voters, according to the Des Moines Register's final poll. But a WMUR poll of New Hampshire also found the president and Romney tied, at 47 percent, in another battleground state: New Hampshire. 

That neither Obama or Romney had managed to open a solid advantage over the other in the final hours of the campaign only raised the stakes for the final series of events on Sunday and Monday. Both Obama and Romney — along with Vice President Biden and Republican vice presidential nominee Paul Ryan — were set to hit the road for another robust schedule tomorrow. Obama was set to travel to Colorado, Florida, and New Hampshire; Romney's schedule would take him to Iowa, Ohio and Pennsylvania.

Updated at 5:50pmET: A rapidly-approaching conclusion loomed over the 2012 election on Saturday, as President Barack Obama, Republican nominee Mitt Romney, their running mates and surrogates swarmed a series of battleground states to make their closing messages.

Obama and Romney each employed a mixture of uplifting, forward-looking rhetoric with attacks on the other during a whirlwind tour of battleground states set to decide the election on Tuesday.

 Slideshow: On the campaign trail

Looking for a catalyzing moment to push past Obama in those swing states, Romney opted to play up the president's comments Friday at a rally, at which he urged supporters to vote as a means of seeking "revenge" against Republicans.

"Yesterday the president said something you may have heard by now that I think surprised a lot of people. Speaking to an audience, he said you know voting is the best 'revenge,'" Romney said. "He told his supporters, voting for revenge. Vote for revenge? Let me tell you what I’d like to tell you: Vote for love of country."

The Obama campaign, in response Saturday afternoon, called the line of attack "very small."

"I think it's interesting that that's the closing argument that the Romney campaign is making," said Obama spokesman Ben LaBolt.

Related: Obama aide explains 'voting is best revenge' comment

The remarks were consistent with Romney's effort to project momentum heading into the campaign's final weekend, riding high after drawing the largest crowd of its campaign at a Friday night rally in Ohio. The Republican ticket has essentially tried to co-opt the themes of "change" from Obama's 2008 campaign as its closing argument now against the president.

But the Romney campaign's outward optimism clashed with new polls giving Obama an ever-so-slight edge in pivotal swing states. New NBC News/Wall Street Journal/Marist polls showed Romney trailing Obama by six points among likely voters in Ohio, and by two points in Florida.

 Related: Polls: Obama stays ahead in Ohio, deadlocked with Romney in Fla.

Republican vice presidential nominee Paul Ryan's trip Saturday afternoon to Pennsylvania, a state which the GOP has only contended in the final days of the campaign, was emblematic of the campaigns' dueling perspectives toward the campaign. The Romney campaign argued it was a sign of surging momentum while the Obama campaign cast the trip as an act of desperation — a Hail Mary effort driven by foreclosed opportunities in other battleground states. (Romney will stop in Pennsylvania on Sunday.)

While the outcome on Election Day is far from assured, a certain wistfulness set in as Obama looked back at his four years in office. He argued his experience as president showed he was someone whom voters could trust, meaning to imply as well that Romney wasn't.

"When you elect a president, you don’t know what kinds of emergencies may happen. You don’t know what problems he or she may deal with," he said. "But you want to be able to trust your president."

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In this composite photo: President Barack Obama points while speaking at a campaign event at Mentor High School in Ohio, and Republican presidential nominee Mitt Romney speaks at a campaign rally in Dubuque, Iowa November 3, 2012.  

And amid the late-breaking attack by Romney meant to cast Obama as embittered, the president told a crowd in Mentor, Ohio: "I don't feel cynical. I feel hopeful."

There were signs that awareness of the campaign's approaching horizon had set in among the Romney campaign as well.

"It was very emotional when I gave my last address by myself, because I hear the voices and the passion of the people out there that are really hurting, and they are etched in my mind and my heart, as they are with Mitt," Ann Romney told the press corps traveling with her husband. "It's been an extraordinary experience."

 Recommended: Ryan travels to Pennsylvania, trying to put state in play

The full range of reflection would have to wait, though, until Wednesday. Obama and Romney — along with their running mates, Vice President Joe Biden and Ryan — each have a long list of stops ahead of them during the remainder of Saturday, Sunday and Monday. Their efforts are met by hoards of Democratic and Republican surrogates, who fanned out across the country as part of a frenzied effort in hopes of  adding a few more swing states to their candidate's column on Tuesday. 

MONTROSE, Colo. -- Just hours after the latest unemployment report was released Friday, Republican vice presidential candidate Paul Ryan attacked President Barack Obama for not living up to his promise of getting more Americans back to work.

Related: Jobs data unlikely to sway undecided voters

"We just got the latest jobs report that voters are going to see before heading to the polls on Election Day. And what we saw today is that the unemployment rate is higher than the day that President Obama came into office," Ryan, the chairman of the House Budget Committee, said. "We are 9 million jobs short than what he said he would accomplish. Look, in the president's campaign for another term, he has offered nothing different and if he is reelected, nothing different is exactly what we would get."

Recommended: Obama, Romney bring their closing arguments to the Midwest 

The U.S. economy added 171,000 jobs in October, according to a Bureau of Labor Statistics Report, and the unemployment rate ticked up to 7.9 percent, still below the important psychological threshold of 8 percent.

In the shadows of the San Juan Mountains, Ryan told voters in the key battleground of Colorado to hold on for just another few days.

"Here’s what it comes down to: we can't afford to wait four more years for real change to get us on the right track. We only need to wait four more days. Four more days and we can do this. Four more days. Four more days and we can get this on the right track," he said at the Black Canyon Jet Center to a cheering crowd.

Recommended: Democrats face very steep climb to 25 House seats they need

The Friday morning rally marked Ryan’s 11th in the Centennial State where Republican presidential nominee Mitt Romney and Obama are in a dead heat to capture the state’s nine electoral votes. According to a CNN/ORC International poll released yesterday, Obama barely edges out Romney, 50 to 48 percent, among the state's likely voters. The two-point lead for Obama is within the polls margin of error.

Romney will hold two events in Colorado Saturday while Ryan returns on Sunday for an event in Castle Rock before Tuesday’s election.

Justin Sullivan / Getty Images

Mitt Romney and Paul Ryan sing along with Janna Ryan as the Oakridge Boys perform during a campaign rally at the Marion County Fairgrounds in Marion, Ohio on Sunday.

Ohio's Republican governor said Sunday that private polls show Republican presidential nominee Mitt Romney beating President Barack Obama in the all-important battleground state of Ohio just as auto industry politics assume a dominant role in the closing days of the campaign. 

Ohio Gov. John Kasich (R) predicted outright that Romney would win Ohio on "Meet the Press" and, with it, the presidential election — a overall contest which Kasich said wouldn't be that close.

"Right now, I believe we're currently ahead. Internals show us currently ahead," he said, referring to the private polling candidates routinely conduct. "Honestly, I believe that Romney is going to carry Ohio."

The governor's show of confidence comes after a week in which Obama and Romney — along with their respective running mates — barnstormed the Buckeye State in hopes of securing the state's 18 electoral votes, which would greatly enhance either candidate's hopes of winning the presidential election.

A Cincinnati Enquirer/Ohio News poll released Sunday and conducted Oct. 18-23 showed the two candidates tied at 49 percent apiece among likely voters in the state. Two other public polls earlier in the week, by CNN/ORC and TIME magazine, showed Obama leading by a small margin.

Romney was set to spend Sunday touring the Buckeye State after canceling a series of stops in Virginia due to the impending Hurricane Sandy; Obama will make a quick trip to Youngstown on Monday before returning to Washington to monitor the hurricane. The president canceled planned stops in northern Virginia and Colorado in the first half of this week. 

Both the president and Romney are battling to turn out their supporters to the polls and shake loose the few remaining undecided voters in a handful of swing states. The Romney campaign has claimed that momentum is on their side, a claim which the Obama campaign argues is a bluff. 

The Romney campaign circulated on Sunday several newspaper endorsements — the Des Moines Register and the Cincinnati Enquirer among them — to argue that the Republican ticket had made inroads in crucial swing states. The Obama campaign responded in kind by sending reporters endorsement editorials from the Youngstown Vindicator and the Toledo Blade, both of which referenced the 2009 auto industry bailout as a point in Obama's favor. 

The auto bailout — which Romney had opposed, memorably, in a New York Times op-ed entitled "Let Detroit Go Bankrupt" — has assumed a central role in the closing days of the campaign, especially as the election plays out largely on a Midwestern, industrial and economically-battered playing field. 

RELATED: Auto politics haunt Romney in NW Ohio

Kasich argued that the auto bailout hadn't actually boosted Ohio's economy as much as Obama would have the state's voters think.

"We are thrilled that we have a strong auto industry," he argued, "but it doesn't account for the growth of 112,000 jobs in our state."

Slideshow: On the campaign trail

Reuters, Getty Images

In the final push in the 2012 presidential election, candidates Mitt Romney and Barack Obama make their last appeals to voters.

Launch slideshow

The Romney campaign also aired a new ad in Ohio touting an endorsement from the right-leaning Detroit News and iconic automan Lee Iacocca, while also making a controversial claim about productions of Jeeps in China.

"Obama took GM and Chrysler into bankruptcy and sold Chrysler to Italians who are going to build Jeeps in China," the ad says in reference to plans by the auto company to build a new production facility in China to sell vehicles in that country. 

The ad is accurate but plays to misinformation that spread earlier this week — partly because Romney had previously voiced the claims — suggesting that Chrysler was planning to move production of all Jeeps to China. The automaker has strongly disputed those reports, though they could have an impact in battleground corners of Ohio like Toledo, a major hub for Jeep production in North America. 

First Read: Romney's Ohio fortunes tied to softening bailout stance

The governors of two other battleground states — John Hickenlooper (D) of Colorado and Scott Walker (R) of Wisconsin —  relied on more traditional fare to make the case for and against their candidates. 

"What are those deductions and tax credits he's going to get rid of?" Hickenlooper asked of Romney's tax reform plan, seizing on the former Massachusetts governor's refusal to specify which loopholes and deductions he would eliminate to finance his proposed tax cuts. 

And Walker, whose contentious collective bargaining reforms sparked a standoff with his state legislature and a recall election which he won, argued that Romney has a track record of working in a bipartisan manner. 

"He's proven that he can do it in a state like Massachusetts," Walker said. 

But neither Walker nor Hickenlooper seemed as confident as Kasich, who predicted that the fate of Ohio's electoral votes — and the election — would be known early on election night. 

"I'm not sure the election's going to be as close as what everybody is talking about today," he said. 

The Daily Rundown's Chuck takes a deep dive into Colorado. What does it take to win the state, and why is it such a critical piece of the president's path to 270?

The economy remains the top issue for voters, and a new set of data released Friday paints a picture of an uneven economic recovery in a series of battleground states.

Of the nine states categorized as "battleground states" by NBC News, five had state unemployment rates below the national unemployment rate of 7.8 percent in September, according to preliminary estimates released Friday by the Bureau of Labor Statistics.

The other four states suffered from a higher-than-average jobless rates, the highest of which was in Nevada; the BLS said that 11.8 percent of Nevadans were unemployed through September, the highest unemployment rate of all 50 states. (One U.S. territory, Puerto Rico, had a higher jobless rate.)

Friday's news is the last series of state-level unemployement data voters will receive before Election Day. One last national jobs report is due Nov. 2, the Friday before voters head to the polls.

President Barack Obama and Republican nominee Mitt Romney have each made jobs the centerpiece of their respective campaigns. The president got a boost earlier this month when the BLS report showed the unemployment rate dropping below 8 percent for the first time in years, disarming Romney of one of his most potent cudgels versus the president.

But as each Obama and Romney travel the country over the next 18 days looking to secure the 270 electoral votes they need to win the White House, economic optimism might be brighter in some states and still dim in others.

The five states with unemployment rates below 7.8 percent included Iowa (5.2 percent), New Hampshire (5.7 percent), Ohio (7.0 percent), Virginia (5.9 percent) and Wisconsin (7.3 percent).

The four battleground states with unemployment rates above the national average are Colorado (8.0 percent), Florida (8.7 percent), Nevada and North Carolina (9.6 percent).

If, for purposes of speculation, Obama were to win the battleground states with jobless rates beneath 7.8 percent along with all of the other states considered more safely in his column, he would win the Electoral College, 288-250.

But politics, of course, are not that simple. For instance, the number of employees on nonfarm payrolls in Ohio actually decreased between August and September, though the unemployment rate dropped from 7.2 percent to 7 percent over the same period.

But as Obama argues that the economy is moving forward and Romney asserts that the recovery has not been sufficiently robust, it's helpful to remember how those arguments might sound different to voters in differing states.

GREELEY, Colo. -- Nearly a week after a feisty debate performance, Vice President Joe Biden is still displaying a high level of energy on the campaign trail.

Campaigning in swing state Colorado for the first time this year, an energetic Biden -- punctuating his remarks with "whoa"s and "c'mon"s -- came equipped with zingers about GOP presidential nominee Mitt Romney's statements about equal pay and immigration during last night's presidential debate at Hofstra University.

"You heard the debate last night," the vice president told a crowd of about a thousand at a warehouse-like expo center in red-leaning Weld County. "When Governor Romney was asked a direct question about equal pay, he started talking about binders. Whoa! The idea that he had to go and ask where a qualified woman was, he just should have come to my house!"

Repeating a criticism from this morning's interview circuit, Biden said that Romney was "a little sketchy" on details last night, as was Republican VP candidate Paul Ryan during the two men's mano-a-mano in Kentucky last week.

"The answers are always the same: 'Maybe. It depends. We'll let you know after the election,'" Biden said of the Romney-Ryan ticket.

In Greeley, where the 2010 Census estimated the Hispanic population was 36 percent, Biden also took aim at Romney's January embrace of "self-deportation" as a solution to address illegal immigration.

"I mean, I don't care what your position is on immigration. Self-deportation?" Biden said to laughter. "Whoa! Every 13-year-old, get up and move, man!"

While he issued a broad salvo about Romney's grasp of foreign policy, Biden did not mention the controversy that erupted after the two candidates tussled over Obama's use of the word "terror" to describe the September 11 attack on the American consulate in Benghazi.

Instead, he poked fun at the Romney team's occasional reference to "the Soviet Union" as well as Romney's expressed concern about Russia as the nation's top geopolitical threat. "Whoa!" he exclaimed. "These guys are kind of in a time warp!"

The vice president travels this afternoon to Reno, NV for another campaign event.

Updated 1:53 p.m. - President Barack Obama is enjoying the help of guest stars in recent TV ads airing in swing states.

The president's re-election campaign released a new ad on Sunday, which aired during some of yesterday's nationally-televised sporting events, featuring actor Morgan Freeman doing voiceover work in a spot about the challenges Obama faced upon taking office.

And on Monday, the Obama campaign released a new ad targeting voters in Ohio, featuring former senator and legendary astronaut John Glenn speaking directly to the camera in support of the president's re-election.

"Growing up in Ohio, you learn to size up a person by their character," Glenn says in the ad. "And that's why I'm supporting President Obama."

The cameos come just 22 days before the election, as the president looks to hold off a potentially resurgent opponent in Mitt Romney, who's making up ground versus Obama after a strong performance in their first debate.

Obama's benefited from celebrity support throughout the campaign, having held a star-studded concert last week in Los Angeles, featuring Katy Perry, Stevie Wonder, Jennifer Hudson, Earth Wind & Fire and Jon Bon Jovi.

Obama is also getting a boost this week from rocker Bruce Springsteen; the boss is campaigning in Cleveland this week alongside another Democratic rock star: former President Bill Clinton.

"This election is a clear choice between two different visions for Ohio and the country. We can have four more years like the last four years, with more policies from President Obama that stifle job growth, hurt energy production, and make it harder for businesses to hire," said Romney spokeswoman Amanda Henneberg. "Or we can choose Mitt Romney, who has a pro-growth vision for the country that will unleash the private sector, utilize our domestic energy resources, and help Ohio – and the rest of the country – experience a real recovery."

Romney has made use of some celebrity support, too. Musician Kid Rock rallied with Paul Ryan last week in Michigan, and, of course, actor Clint Eastwood nearly stole the spotlight from Romney at the Republican National Convention in August with a 15-minute routine with an empty chair meant to represent Obama.

But it's quite another thing to put these celebrities on television in the home stretch of a campaign.

Outside groups are getting in on the celebrity action, too. The liberal group MoveOn.org Political Action released a new ad set to run in Colorado and Virginia featuring actresses Scarlett Johansson, Kerry Washington and Eva Longoria (the last of whom is an official co-chair for the Obama campaign) speaking about reproductive rights.

Ed Andrieski / AP

President Barack Obama waves as he arrives at a campaign rally in Denver, Thursday, Oct. 4, 2012.

DENVER -- A fired-up President Barack Obama spoke to a crowd of more than 12,000 at a Denver campaign event Thursday and seemed to exude the energy and aggressiveness that many of his supporters felt was missing at last night's presidential debate.

Trying to rebound from what many called a listless performance last night, Obama argued today that the Mitt Romney who appeared at the debate was not the “real Mitt Romney.”

First Read: Romney helps himself
 
“When I got on stage, I met this very spirited fellow who claimed to be Mitt Romney,” he said. “But it couldn’t have been Mitt Romney, because the real Mitt Romney has been running around the country for the year, promising $5 trillion dollars in tax cuts that favor the wealthy. The fellow on stage last night didn’t seem to know anything about that.”
 
The president dedicated the first part of his speech to retroactively rebutting Romney’s debate talking points.

Last night, Romney said his plans to trim the deficit wouldn’t mean teacher cuts: “I reject the idea that I don’t believe in great teachers or more teachers. Every school district, every state should make that decision on their own.”
 
Romney had the final word on the matter last night, but today Obama told his supporters: “The real Mitt Romney said we don’t need anymore teachers in our classrooms ... But the fellow on stage last night, he loves teachers, can’t get enough of them.”
 
Last night, Obama also missed an opportunity to highlight his opponent’s personal tax records after Gov. Romney said, “I’ve been in business for 25 years. I have no idea what you’re talking about. I maybe need to get a new accountant ... but the idea that you get a break for shipping jobs overseas is simply not the case."
 
Today, Mr. Obama fired off this retort: “We know for sure it was not the real Mitt Romney because he seems to be doing just fine with his current accountant.”

Kevin Lamarque / Reuters

President Barack Obama greets supporters during a campaign rally in Denver on Oct. 4, 2012.

And while Romney drew a lot of public criticism for suggesting his deficit reductions would include stripping federal funding for PBS -- and by extension “Big Bird” -- Obama did not challenge him on the point until today: “He said he’d eliminate funding for public television... I mean thank goodness someone is finally getting tough on ‘Big Bird.’ ”
   
The crowd responded to the president’s jabs with loud cheers, but for many the disappointment from the president’s debate performance had already set in. 

Axelrod: 'I'm sure we will make adjustments'

Bruce Shaffer of Boulder told NBC News, “I wanted him to be more of a president and sound strong, sound confident and be more of the leader we need.”

President Barack Obama and GOP presidential candidate Mitt Romney

President Barack Obama and Republican nominee Mitt Romney take the stage at the University of Denver tonight for the first of three debates in the 2012 presidential race. Click here to watch the livestream.

Presidential debates are as closely scrutinized for gaffes as for policy pronouncements, something President Barack Obama and Republican presidential nominee Mitt Romney know all too well.

Both candidates can arguably trace some of their political success to opponents’ missteps in debates, and both Obama and Romney are acutely aware that a cringeworthy debate moment can do as much – if not more – to alter the trajectory of a campaign as a good zinger.

The Obama and Romney campaigns have downplayed expectations for their respective candidates’ debate performances, almost to the point of comedy. But both candidates know that it’s better for them to exceed low expectations than to have to clear a high bar.

Romney’s debate shortly before the election in his 2002 bid for governor offers an instructive example. Romney entered the showdown trailing Democrat Shannon O’Brien by a few points in most polls, but the two of them failed to land many blows for much of the debate until they encountered a seemingly mundane question about parental consent for minors seeking abortions.

O’Brien responded to a question from the moderator (which, as a matter of full disclosure, was my father, Tim Russert) by saying she favored lowering the age at which girls need parental consent to obtain an abortion (18) to match the legal age of consent in Massachusetts (16).

“The age of consent for having sexual relations is lower than the age of 18, so I certainly think if someone is able to engage in that activity that they should be adult enough to make the decision.”

Romney said he would leave the current laws unchanged. O’Brien’s response to a follow-up point, about how Massachusetts minors needed parental consent to get a tattoo, offered a more lasting debate moment.

“You want to see my tattoo?” she jokingly said.

The incident hurt O’Brien with independents and Catholics in Massachusetts with so little time to recover before the election. Massachusetts political analyst Jon Keller of CBS Boston WBZ-TV recounted the moment as O’Brien’s downfall in his book titled “The Bluest State.” 

“O’Brien’s dismissal of parental consent rights and her flip tattoo comment caused a sensation, and her remarks dominated talk-radio chatter in the campaign’s final days. On Election Day, Romney romped. He carried 56 percent of independents as well as 52 percent of self-described moderates. He mopped up with Catholics, tripling the margin of the previous Republican governor.”

Romney, of course, went on to serve as governor of Massachusetts before twice seeking the Republican presidential nomination.

In his 2012 bid for the GOP nod, Romney certainly re-learned lessons about navigating presidential debates. His line about why he wouldn’t employ a landscaping firm that employed illegal immigrants (“I’m running for office, for Pete’s sake!”) and his misbegotten $10,000 bet to Texas Gov. Rick Perry proved to be lasting moments to the former Massachusetts governor’s detriment in the debate.

And as if to underscore how damning a single lapse can be, Romney is certainly familiar with Perry’s own gaffe – the “oops” moment when the Texas governor simply forgot which three federal agencies he’d promised to eliminate.

The lessons are familiar for Obama, too. He saw when then-Sen. Hillary Clinton struggled with an answer about providing drivers licenses to illegal immigrants, a difficult moment that hurt her in her protracted primary battle versus Obama.

When asked at an Oct. 30, 2007 primary debate at Drexel University whether she backed a plan by the state of New York to grant drivers licenses to illegal immigrant, Clinton gave an elusive answer that seemed to further muddle her opinion on the issue.

She said: “You know, this is where everybody plays ‘gotcha.’ It makes a lot of sense. What is the governor supposed to do? He is dealing with serious problems. We have failed. And George Bush has failed. Do I think this is the best thing for any governor to do? No. But do I understand the sense of real desperation, trying to get a handle on this? Remember, in New York, we want to know who's in New York. We want people to come out of the shadows.”

Clinton had been seen as the frontrunner for the Democratic nomination prior to that point, but her opponents – which included Sen. Chris Dodd (D-CT), former Sen. John Edwards (D-NC) and Obama – to pounce.

“Well, I was confused on Senator Clinton's answer,” Obama said. “I can't tell whether she was for it or against it. And I do think that is important. One of the things that we have to do in this country is to be honest about the challenges that we face…Immigration is a difficult issue. But part of leadership is not just looking backwards and seeing what's popular or trying to gauge popular sentiment. It's about setting a direction for the country. And that's what I intend to do as president.”

John Heilemann and Mark Halperin, authors of the definitive book about the 2008 election, “Game Change,” described the incident in that work:

“But whatever the confluence of causes and effects, the damage to the front-runner from the Drexel debate and its aftermath was more severe than anyone in Hillaryland knew. The inevitable candidate was suddenly revealed as vulnerable. The flawless campaign looked fallible. The Clinton Juggernaut had a hole in its hull and water was rushing in.”

In a span of one debate question Clinton went from the inevitable nominee to fighting a long, drawn out primary that eventually ended in a humbling defeat and allow Obama to become the Democratic nominee and eventually president.

So while the conventional wisdom is that one debate won’t totally alter this election, it should be noted that debates can significantly alter the trajectory of a race and even decide them. The two men debating in Denver tonight know that better than anybody.