As the clock ticked down to Tuesday's vote, Romney's efforts included a surprise foray into Pennsylvania, a Democratic-leaning state that Republican strategists say is breaking his way.

"We're taking back the White House because we're going to win Pennsylvania," Romney told a crowd of up to 30,000 who had gathered on a farm in frigid weather. Obama advisers dismissed the trip as a sign of desperation from the challenger less than 48 hours from election day.

And yet a valuable character witness, former president Bill Clinton, will headline four rallies for Obama on Monday in Pennsylvania, to counter Romney's late push there.

Democrats said they were confident of Obama's small but steady lead in key swing states, but acknowledged that everything now depends on getting the vote out.

Obama flew to New Hampshire to reprise a buddy act from the night before with Clinton, which saw the popular former president place his economic legacy on the younger leader's shoulders.

On a demanding swing, the Democratic incumbent also traveled to Florida, Ohio and Colorado before touching down in Wisconsin in the early hours on Monday.

Exhaustion began to show on both candidates this past weekend as they keep up frenetic paces straight into Monday, when each performs another multi-state crisscross that would make any frequent flyer proud.

Obama begins in Wisconsin, continues to Ohio and then to Iowa, the state where Obama began his presidential run in 2008, before returning to his hometown of Chicago.

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