The political pace quickened on Monday even without the customary clash of rallies and rhetoric. Romney's allies put down $1.2 million for a last-minute television ad campaign designed to make Pennsylvania competitive - or at least appear so - and the roll of early voters swelled past 15 million in scattered states.
With the race in its final full week, most national polls showed the two presidential rivals separated by a statistically insignificant point or two, although others said Romney had a narrow lead for the overall popular vote.
But the election will be won or lost in the nine most competitive states. Republicans claimed momentum there, but the president's high command projected confidence. And Romney's increasingly narrow focus on Iowa, Wisconsin and Ohio suggested he still searched for a breakthrough in the Midwest to deny Obama the 270 electoral votes needed for victory.
The president changed roles quickly during the day, highlighting the advantages of the incumbency - as long as events go smoothly. He scrapped a morning campaign appearance in Florida, boarded Air Force One for a bumpy flight to the nation's capital and appeared before reporters in the White House not long afterward.
"We're making sure that food and water and emergency generation is available for those communities that are going to be hardest hit," he said. At the same time, he soberly warned that heeding evacuation orders from local authorities was paramount for those in the storm's path.
"Do not delay. Don't pause. Don't question the instructions that are being given, because this is a serious storm and it could potentially have fatal consequence if people haven't acted quickly," he said.
The president didn't mention the campaign in his prepared remarks, and when he was asked how the storm might affect the election, he said he wasn't thinking along those lines. "I'm worried about the impact on families, and I'm worried about the impact on our first responders. I'm worried about the impact on our economy and on transportation," he said.
Romney went ahead with part of his campaign schedule, although he blended his appeal for political support with one for his backers to make a donation to the Red Cross or other relief agencies "in any way you can imagine to help those in harm's way."
"Do your very best to help," he implored as his aides spread the word he would cancel an evening appearance in Wisconsin and a full day of campaigning Tuesday because of the storm.
He received an update on federal storm response efforts in a phone call with the deputy director of the Federal Emergency Management Agency and other officials.
However, the campaign said Romney "believes that states should be in charge of emergency management in responding to storms and other natural disasters in their jurisdictions" and "are in the best position to aid affected individuals and communities and to direct resources and assistance to where they are needed most. This includes help from the federal government and FEMA."
Nearing the end of a brawl of a campaign, both Romney and the president said they hoped Americans would work together to help those in need - and an unscientific sample of voters said they liked what they were hearing.
Mike Beauregard, the owner of a cooking utensil store in Concord, N.H., said he was glad the president and Romney were cutting short their campaign trips. "The last thing first responders need is for these folks to be running around," he said, describing himself as a political independent who leans Republican.
Chuck Sikes, manager of a furniture store in Concord, also said both candidates did the right thing. A self-described Obama supporter, he said the president "would have been criticized if he had continued campaigning as not caring for people, yet others will criticize him for returning to Washington as making it a photo op. You're damned if you do, damned if you don't."
The machinery of the campaign ground on. According to the United States Elections Project at George Mason University, about 15 million ballots already have been cast, including 1.8 million in Florida and 1.5 million in North Carolina.
Democratic early voters so far outnumber Republicans in Ohio, Iowa, North Carolina and Nevada, while the reverse is true in Colorado. The two sides are at rough parity in Florida. No votes will be counted until Nov. 6.
The expansion of television advertising into Pennsylvania began with Restore Our Future, the group that was instrumental to Romney's success in the primaries and has worked to defeat Obama. The commercial says a "new normal" has developed as a result of the president's economic policies, where unemployment is high, "millions of Americans have simply given up, where our children will grow up under the weight of crushing debt in a world where America is no longer the leader."
Jim Messina, Obama's campaign manager, told reporters to expect an ad in response. "They are not close in Pennsylvania. We're going to win Pennsylvania, but we aren't taking anything for granted." Vice President Joe Biden is expected to campaign in the state before Election Day.
Yet another controversy erupted over a late-campaign television ad the Romney campaign was airing in parts of Ohio.
It says the Republican challenger will do more to support the auto industry than the president. "Obama took GM and Chrysler into bankruptcy and sold Chrysler to Italians who are going to build Jeeps in China," the narrator says.
The commercial does not mention that under the 2009 auto industry bailout, the Obama administration made sure that billions in federal loans were available to GM and Chrysler to allow them to emerge from bankruptcy and continue operations, a course that Romney opposed.
Additionally, while Chrysler may move some of its Jeep product line to China, that doesn't threaten production in the United States, as the ad seemed to suggest.
Obama's campaign countered with a commercial that opens with a photo of a shuttered factory, then shows a New York Times column that Romney wrote in 2008 that was headlined: "Let Detroit go Bankrupt."
Says the narrator, "When the auto industry faced collapse, Mitt Romney turned his back. ... And now, after Romney's false claim of Jeep outsourcing to China, Chrysler itself has refuted Romney's lie."
With Obama at the White House at least through Tuesday, former President Bill Clinton campaigned solo in Florida, then joined with Biden in Ohio. Obama's campaign booked Clinton into Minnesota, Iowa, Colorado, Ohio, Virginia, New Hampshire and Wisconsin for the race's final days.
Biden events in Ohio on Tuesday and in Pennsylvania on Thursday were canceled because of the storm.
Romney's running mate, Rep. Paul Ryan, campaigned in Florida, and like the man at the top of the ticket, urged supporters to help those in need. "Here at home, people are packaging supplies at our victory centers throughout Florida. Swing by, give a hand," he said.
Associated Press writers Steve Peoples in Avon Lake, Ohio, Brian Bakst in St. Paul, Minn., Norma Love in Concord, N.H., Beth Fouhy in New York, Ken Thomas, Julie Pace and Jim Kuhnhenn in Washington and AP Auto Writer Tom Krisher in Detroit contributed to this report. Espo reported from Washington.