Obama was scheduled to campaign Tuesday evening in Wisconsin, though that too was in flux.
Romney canceled three events in Virginia on Sunday and planned to spend the day campaigning with running mate Paul Ryan in Ohio.
If bad weather keeps people in hard-hit battleground states from going to the polls, it could mess up the campaigns' carefully crafted get-out-the-vote efforts.
Jennifer Psaki, Obama's campaign spokeswoman, said the Democratic ticket was urging people to vote early when they can, especially if it helps them get to the polls before the storm.
"Safety comes first," she said. "And that's the case with early voting as well."
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