(Bloomberg News) President Barack Obama and Mitt Romney are both running against history -- the only question now is who will defy it to win the presidency.

Obama is seeking to overcome the drag of high unemployment and economic weakness that has frustrated predecessors' re- election bids, while his Republican rival Romney reaches for an upset to propel him beyond his party's standing and swamp an electoral map stacked against him on the final day of the presidential race.

A victory for Obama, to whom the contest has tilted in recent days, would make him the first president in two decades to be re-elected with a jobless rate above 6 percent -- and only the second since World War II.

For Romney, a win would mark one of the few times that a challenger heading a party regarded less favorably than the one holding the White House has prevailed -- and a triumph over Electoral College math that has shown a slim edge for Obama in recent days.

With the hours ticking down until polls close, Romney scheduled last-minute visits to Ohio and Pennsylvania today after voting in Boston, in a final effort to shake loose enough votes to put him over the top.

"The same course we're on isn't going to lead to a better destination," Romney told supporters at George Mason University in Fairfax, Virginia, yesterday. "Unless we change course, we may also be looking at another recession."

'Go Vote'

Obama, who voted early in Chicago last month and plans an Election Night party in his hometown, prodded his supporters to "go vote" as his campaign worked an elaborate turnout plan five years in the making.

"You may not agree with every single decision that I've made," the president told voters yesterday in Columbus, Ohio. "You know that I mean what I say, and I say what I mean."

The final polls in a campaign that has seen large swings in public opinion almost unanimously pointed to momentum in Obama's favor. Yet after the most costly presidential contest in history at $2.6 billion -- as well as one of the longest -- the surveys also suggested the race remains exceptionally close until the end, with the candidates vying for advantage both nationally and in crucial battleground states.

Political Odysseys

They landed there after political odysseys that saw both candidates morph into a mirror image of the person they first presented to voters. Obama, who campaigned in 2008 as an underdog and transformational figure promising hope and change, ran his 2012 bid on a more modest pledge of continuing steady if frustratingly slow progress -- a theme more in keeping with the 7.9 percent rate of unemployment recorded in the last jobs report before the balloting.

"You've seen the gray hair on my head to show you what it means to fight for change," Obama said in Madison, Wisconsin. "And you've been there with me.  And after all we've been through together, we can't give up now."

Romney, the former Massachusetts governor, having long- since abandoned his one-time support for abortion rights and a government health-care mandate, began the year branding himself "severely conservative" as he slogged through a crowded Republican primary in which party activists put a premium on ideological purity. He ends it calling himself a bipartisan consensus-builder who will bring about "real change" -- the kind Obama promised yet didn't deliver.

Yard Signs

"I'd like you to reach across the street to that neighbor with the other yard sign -- and we'll reach across the aisle here in Washington to people of good faith in the other party," Romney said in Fairfax, Virginia.

The president and his challenger were both responding to developments beyond their control, said historians who watched the race.

"When Obama came to office, people were framing him as the new Franklin Roosevelt -- he was going to come in and fix this economic mess and offer a new beginning," said political historian Beverly Gage of Yale University. "It's pretty remarkable how different this election is now, and how really vulnerable he has seemed all along, compared to something like the 1936 election. Obama has ended up owning the economic crisis in a way that someone like Roosevelt didn't seem to, and that has been his biggest stumbling block."

Jobless Rate

The unemployment rate, at 7.8 percent as Obama took the oath of office on Jan. 20, 2009, spent 43 consecutive months above 8 percent before settling back to 7.9 percent in the latest jobs report on Nov. 2.

Republican Ronald Reagan is the only president to have been re-elected since World War II with a jobless rate above 6 percent. The rate was 7.2 percent on Election Day 1984, having dropped almost 3 percentage points in the previous 18 months. Through October this year, the rate has declined 1.1 points in the same period under Obama.

It was impossible for Obama to rekindle the sense of history that pervaded his first campaign, said presidential historian Robert Dallek.

"There's only one first time for being the first African- American to win," Dallek said in an interview. "It's faded, it's four years later. You can't just generate the kind of excitement and enthusiasm that Obama could the first time -- circumstances change."

Primary Battle

Romney, too, had the challenge of running at a time ill- suited to his political profile as the former governor of a Democrat-dominated state who had previously been known more as a pragmatist than a party soldier.

"It's been very difficult for him because of the primaries," Dallek said. "He was up against so many people who were so much to the right of him, and he had to protect his flank, because that's where his party is."

An NBC News/Wall Street Journal Poll conducted Nov. 1-3 showed the Democratic Party's brand in better shape than Republicans'. Forty-three percent had a positive view of Democrats compared to 42 percent holding a negative one, while 39 percent viewed Republicans favorably compared to 44 percent who saw them unfavorably. It has been rare for a presidential candidate whose party has the weaker image to prevail in the race for the White House.

Still, Romney appeared to be benefiting from intense Republican sentiment for turning out Obama. A CNN/ORC International poll released Nov. 4 showed a tied contest, with 49 percent of likely voters supporting each candidate, and suggested his backers remain more enamored with the idea of firing Obama than they are of hiring Romney.

Motivations Gap

While 86 percent of Obama's backers said they were voting for him because they genuinely like and agree with him and 12 percent said they were voting against Romney, more than a third of the Republican's supporters -- 37 percent -- said they were supporting him to vote against the president.

The campaign was shaping up to be the costliest in U.S. history, although it wasn't clear whether the billions of dollars spent on television advertising in the most competitive states would amount to a net advantage for either side.

Each campaign also used technology and especially social media in unprecedented ways to influence the contest. Obama, who pioneered the use of social media in presidential politics four years ago when Facebook Inc.'s social network was one-tenth its size and before Twitter was widely used, employed both this year to boost fundraising, recruit volunteers and to try to drive media coverage. Romney's camp used them to mobilize volunteers and boost turnout. On the eve of the election, Obama had 31.8 million Facebook page "likes" to Romney's 12 million.

Hispanic Power

The contest also was testing the potency of Latino voters, the fastest-growing portion of the electorate, and one that is expected to back Obama by a sizable margin.

A poll released yesterday by impreMedia and Latino Decisions found that 73 percent of likely Latino voters planned to vote for the president, compared to 24 percent for Romney.

That would be a greater proportion for Obama than former President Bill Clinton won in his 1996 re-election, when 72 percent of Latino voters backed him. It would also be a significant drop-off in support among Latinos for the Republican; Arizona Senator John McCain, the 2008 nominee, won 31 percent of the Latino vote.

In appearances last night, the candidates pressed their closing arguments for why each should be elected. Speaking at a final rally in Des Moines, Iowa, Obama's voice cracked as he returned to a phrase from the 2008 campaign -- "change the world" -- that he's deliberately kept from 2012 rallies.

Closing Messages

After calling out his rival at rallies earlier yesterday, Obama didn't mention Romney by name in his address to an estimated 20,000 supporters in Des Moines.

"From the coastlines of Florida to Virginia's rolling hills, from the valleys of Ohio to these Iowa fields, we will keep America moving forward," the president said.

Romney, meanwhile, delivered his message to more than 10,000 supporters in Manchester, New Hampshire, where he was introduced by musician Kid Rock, who played the campaign's theme song -- "Born Free" -- as red and blue laser lights shot out over the crowd.

"This is much more than our moment. It's America's moment of renewal and purpose," Romney said. "One final push and we'll get there."