The 2012 race headed into a turbulent last full week Sunday as President Obama and opponent Mitt Romney made final arguments to voters while their campaigns dealt with uncertainty spawned by a menacing storm that has already hindered early voting in the extraordinarily close contest.

Obama, trying to stay ahead of Hurricane Sandy, flew out of Washington on Sunday evening for a Monday rally in Orlando. But he later canceled the appearance and the campaign said he will skip a rally later in the day in Youngstown, Ohio, to return to the White House to monitor the storm. Officials said the event will go forward as scheduled with Vice President Biden and former president Bill Clinton. A Monday rally in Prince William County was scuttled.

Obama on Monday morning also canceled a Tuesday campaign event in Green Bay, Wis.

Romney scrubbed events in Virginia on Sunday to join running mate Paul Ryan on an Ohio bus tour. A rally Tuesday in New Hampshire has also been canceled, campaign officials said.

Even under normal circumstances, the last days of a presidential campaign can be a flurry of improvisation. Plans are scrambled and events added to the schedule at the last minute as candidates try to wring maximum advantage from their final opportunities to appeal directly to voters. Hurricane Sandy, headed for landfall on the Mid-Atlantic coast Monday, adds another unpredictable factor to the endgame.

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The latest Washington Post-ABC News tracking poll shows the race holding at a statistical dead heat, with Romney ahead 49 percent to 48 percent.

Both campaigns are scrambling to evaluate Sandy’s potential impact on swing states such as Ohio, North Carolina, Virginia and New Hampshire. Obama adviser David Axelrod said Sunday that it could reduce turnout and hurt Obama’s reelection chances.

“Obviously we want unfettered access to the polls, because we believe that the more people come out, the better we’re going to do,” he said on NBC’s “Meet the Press.” “And so, to the extent that it makes it harder, that’s a source of concern.”

Romney senior adviser Kevin Madden said that plans could change depending on the severity of the storm and that “our top priority is the safety and security” of those who may be in harm’s way.

“We’ll have to monitor the storm in case we need to make any adjustments,” he said. “But it’s hard to predict right now.”

For the moment, Romney and Ryan are expected to keep campaigning separately in Ohio, Florida, Wisconsin and Iowa.

The impending storm has already disrupted early voting in the Washington region. D.C. election officials canceled early balloting on Monday, as did Maryland Gov. Martin O’Malley (D), citing concerns about the ability of voters to travel or reach polls in areas under mandatory or voluntary evacuations. He said the lost day could possibly be made up Friday.

More than 20 percent of Maryland’s electorate was expected to cast ballots during the scheduled six days of early voting. While there is little doubt that Obama will carry the state, the storm could affect the outcome of ballot measures on same-sex marriage, the expansion of casino gambling and the extension of tuition breaks to some illegal immigrants.

Sandy will also hamper in-
person absentee voting in at least some parts of Virginia on Monday. Four jurisdictions on the Eastern Shore and southeastern Virginia — Accomack, Portsmouth, Virginia Beach and Surry County — announced Sunday that they would not hold early voting Monday, and more cancellations were expected overnight, said Nikki Sheridan, spokeswoman for the Virginia State Board of Elections.

Sheridan advised voters to call ahead to check the status of their local elections office.

The two candidates in the state’s fiercely contested U.S. Senate race planned — as of Sunday evening — to push forward. Former governor Timothy M. Kaine (D) was still scheduled for events in Greene, Culpeper and Fauquier counties on Monday morning and afternoon. His Republican rival, former governor and senator George Allen, was set to visit a small business in Springfield on Monday morning.

Kaine and Allen are asking supporters to take down yard signs before they take flight.

“Don’t forget that yard signs . . . can blow around in strong winds, causing dangerous conditions and damage,” Allen said in an e-mail to his supporters.

“The last thing we want is for yard signs to become projectiles,” Kaine said in his ­e-mail.

For Obama, the storm’s challenge is a delicate one: to function as an effective commander in chief while waging a fight for his political life — and to avoid being seen as placing politics over the needs of storm-damaged areas and their residents. Before leaving for Florida on Sunday, he visited the headquarters of the Federal Emergency Management Agency, where he was briefed by top officials and held a conference call with mayors and governors from areas in Sandy’s path.

“This is a serious and big storm,” Obama told reporters after the briefing. “And my first message is to all the people across the Eastern Seaboard, Mid-Atlantic, going north, that you need to take this very seriously.”

Obama added that he promised local officials they would have “anything they need.”

“And we’re going to cut through red tape,” he said. “We’re not going to get bogged down with a lot of rules.”

Romney will need to respond to storm damage but avoid the appearance of exploiting it for political gain. On Sunday, Romney’s Virginia staff loaded relief supplies onto the campaign bus at its Arlington County headquarters. It also asked supporters to bring bottled water, beef jerky, granola bars and other nonperishable foods to offices around Virginia.

The Republican candidate was in Ohio on Sunday. The final Akron Beacon-Journal/Ohio News Organization poll there showed movement toward Romney in the past month. It put the race tied at 49 percent, a shift from Obama’s five-point lead in September.

“This is an election about change,” Romney told supporters Sunday in Celina, part of a northwest region of the state that Republican candidate John McCain won handily in 2008. The Romney campaign wants to maximize turnout in the GOP stronghold.

“The president thinks this is a time to just keep on doing what we’ve been doing,” Romney said. “Do you want more of the same, or do you want change?”

“Change!” the crowd roared back.

Speaking ahead of Romney, Ryan rallied the crowd with a cheer of “nine more days.”

“We will be debating this for nine more days,” he said. “And then on November the 6th, you decide. Our obligation to you is to give you, our fellow citizens, a very clear choice. . . . November 6th is the day, but I’d like to ask you to think about November 7th for a moment.”

He continued: “We can either have four more years of the same that are just like the last four years, or we can wake up and we can see that we just elected a leader to get our country back on the right track.”

Both campaigns said they expect their Ohio field operations to continue at full force, weather notwithstanding.

Jessica Kershaw, a spokeswoman for Obama’s effort in Ohio, said the campaign is not anticipating the weather will affect early voting or get-out-the-vote efforts in the all-important battleground.

Chris Maloney, the Romney campaign’s Ohio spokesman, said, “Neither snow nor rain nor heat nor gloom of night stays our grass-roots organization from the swift completion of their tasks to make Barack Obama a one-term president.”

Aaron Davis, Laura Vozzella, Ed O’Keefe, Rosalind S. Helderman and David Nakamura contributed to this report.