Obama ditched plans to appear with ex-president Bill Clinton in Florida to steer a huge government relief effort as high winds and torrential rains began to lash the northeastern United States.
Millions of people faced the prospect of damage from snapping trees, severe flooding and power outages, including in some key swing states like Virginia, where Sandy's "October Surprise" may have an unpredictable electoral impact.
Grabbing a chance to leverage the built-in advantages of incumbency, Obama made clear his focus, until Sandy had barreled through, was the safety of Americans, not his own immediate political fate.
"Obviously my first priority has to be to make sure that everything is in place for families," the president told campaign workers in Florida late on Sunday.
"That's going to be putting a little bit more burden on folks in the field, because I'm not going to be able to campaign quite as much over the next couple of days."
The president had been due to appear in Florida, Ohio and Virginia with the popular former Democratic president on Monday, and also scotched plans to head west to Colorado, another swing state, on Tuesday.
Republican Mitt Romney also altered his plans as he tried to drive recent momentum right up to polling day on November 6, seeking to fracture Obama's "firewall" of midwestern states and deprive him of a second term.
The Republican instead canceled rallies in storm-threatened Virginia and went instead to inland Ohio, the Midwestern epicentre of the unpredictable final week battle for the White House.
He was due to spend Monday on the stump in Ohio and Iowa, though will likely tame the vehemence of his message, to avoid accusations he is playing politics while Obama hovers above the fray and shows leadership.
Romney did make an attempt to inject himself into what is likely to be days of news coverage dominated by Sandy's assault, in which the president is also likely to play a prominent role.
"Tonight, Ann and I are keeping the people in Hurricane Sandy's path in our thoughts and prayers," Romney said in an email message to supporters.
"I hope that if you can, you'll reach out to your neighbors who may need help getting ready for the storm — especially your elderly neighbours," he said, and asked backers to bring election yard signs inside.
"I'm never prouder of America than when I see how we pull together in a crisis. There's nothing that we can't handle when we stand together," Romney said.
The storm, expected to be at its most severe Monday and Tuesday, was the latest manifestation of the "October Surprise" – the fabled late-campaign news event with the potential to sway the outcome of a US election.
Its immediate political impact was unpredictable, but it was expected to bring dire conditions to Virginia and also could impact other swing states including Ohio and New Hampshire, and depress early voting elsewhere.
"Obviously we want unfettered access to the polls because we believe that the more people come out, the better we're going to do," senior Obama advisor David Axelrod told CNN.
Romney aide Kevin Madden told reporters his boss had already got his message across to those in the hurricane's path and said the safety of voters and their families was now the priority.
"I wouldn't even want to even trivialize it by talking about the state of the race when you have so many people right now that are going to be adversely impacted by the storm," he said.
Even as the storm approached, bruising rhetoric flared between the rival camps, and supporters of both men suffered a roller coaster ride of conflicting emotions as opinion polls see-sawed in crucial battlegrounds.
Romney got good news on Sunday when a poll showed him tied in all-important Ohio and he captured the endorsement of the Des Moines Register newspaper in Iowa, a state cherished by Obama as the cradle of his 2008 presidential run.
But a new poll in Virginia by the Washington Post and ABC News had Obama leading by four points, compared to previous surveys showing a tied race.
Romney leads by a few points in some national polls of the popular vote, but Obama appears to be clinging to a narrow advantage in the state-by-state race to 270 electoral votes needed to secure the White House.
But Obama was up one point, a swing back to the president of three points from last week, in the latest GWU/Politico/Battleground poll.
Republican party chairperson Reince Priebus hit back at claims from Democrats that Romney's momentum was leveling off and argued that key states like Ohio and Wisconsin were beginning to swing towards the challenger.
"They're not where they were in 2008. We're far ahead of where we were in 2008. Our ground game is better than their ground game," Priebus said on Fox News Sunday.
Conventional wisdom holds that undecided voters break towards a challenger late in the race, fueling Republican hopes of an eleventh hour wave for Romney that could crest at the White House.
But Obama's campaign counters that some pollsters and Republicans are underestimating both the likely turnout on November 6, and the proportion of minority voters who favour Obama. – Sapa-AFP