Obama cancelled a third straight day of campaigning, calling off appearances scheduled Wednesday in Ohio, the most important of the battleground states. He will remain in Washington to monitor the storm and the federal response.
Obama had already cancelled events Monday and Tuesday to manage the vast emergency that hit the heavily populated region between Washington and Boston and stretched toward Chicago and the Midwest. Vice-President Joe Biden joined Obama in shunning campaign events.
Romney and running mate Paul Ryan initially announced they were cancelling events out of sensitivity for the millions of American's in Sandy's path. But Romney went forward with a planned event in Ohio, though it focused on storm relief. Ryan cancelled three Colorado appearances.
Both candidates sought to avoid the appearance of putting politics above Americans' more immediate worries over flooding, power outages, economic calamity and personal safety.
With the outcome of the Nov. 6 election likely to be decided by the thinnest of margins, the storm will dominate news coverage and distract many millions of voters in the critical few days left for the candidates to win over those who remain undecided.
"When the nation's largest city and even its capital are endangered, when so many people are in peril and face deprivation, it's hard to get back to arguing over taxes," said historian and presidential biographer Douglas Brinkley.
Obama declared a "major disaster" in New York City and parts of New Jersey on Tuesday after being updated throughout the night.
He kept in frequent touch with leaders of affected states, prompting the highly partisan Republican governor of New Jersey, Chris Christie, to offer rare high praise.
"The president has been excellent at this," said Christie, a frequent Obama critic and Romney campaigner. "It's been very good working with the president and his administration."
In a brief outing to Red Cross headquarters on Tuesday, Obama warned that the flooding from the storm was not finished. He offered his thoughts and prayers to those affected and told them "America is with you."
In Ohio, Romney told an audience that Americans have "heavy hearts" because of suffering along the East Coast. He collected bags of relief goods from supporters and didn't mention Obama in his brief remarks.
Romney refused to answer repeated shouted questions from reporters about how he would run the Federal Emergency Management Agency as president. He said during the Republican primary race that he wants to return control of some federal functions to the states.
Asked if Romney favours additional federal aid to help recover and rebuild from Sandy, Romney spokeswoman Amanda Henneberg responded: "A Romney-Ryan administration will always ensure that disaster funding is there for those in need. Period."
The storm wasn't entirely off limits from politics. Campaigning on Obama's behalf in Minnesota, former President Bill Clinton resurrected a line from Romney's Republican convention speech to suggest that he was flippant about Obama's advocacy of climate change legislation.
At the late August convention, Romney ridiculed Obama as someone who "promised to begin to slow the rise of the oceans and heal the planet. My promise ... is to help you and your family."
Noting how oceanfront cities are coping with rising waters more frequently, Clinton said on Monday: "In my part of America, we would have liked if someone had done that yesterday."
While officials in Obama's Chicago-based campaign had hoped he would be in battleground states every day this week, they said they weren't losing any ground by having him in Washington. Obama was still getting local media coverage because of his work on the storm. And aides said Clinton's active campaign schedule this week was helping to boost Democratic voter enthusiasm.
As of Tuesday afternoon, there were no plans to cancel Obama's campaign rallies Thursday in Nevada, Colorado, and Ohio, though officials said they continued to monitor the storm. The president may try to make up for lost time by adding more events to an already busy schedule this weekend and into next week, but those plans were still being finalized.
Most national polls showed Obama and Romney separated by a statistically insignificant point or two, although some said Romney had a narrow lead for the overall popular vote.
The election will be won or lost in the nine most competitive states that are not reliably Republican or Democratic. Republicans claimed momentum in those states, but the president's campaign projected confidence. 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 is not chosen by the nationwide popular vote, but in state-by-state contests that allocate electoral votes. Each state gets one electoral vote for each of its seats in the House of Representatives, as determined by population, and two electoral votes for each of its two senators. That means there are 538 electoral votes, including three for Washington, D.C. The winning candidate must have 50 per cent, plus one, or 270 votes.
Obama is ahead in states and Washington, D.C., representing 237 electoral votes; Romney has a comfortable lead in states with 191 electoral votes.