Mrs. Clinton will appear in Michigan, a state dense with working-class voters. She lost the Democratic primary contest there to Senator Bernie Sanders of Vermont. President Obama will also head to Michigan, making a stop in Ann Arbor to boost support among the Democratic base.
Mr. Trump will visit four states: Florida, North Carolina, Pennsylvania and New Hampshire.
On Sunday, the F.B.I. director, James B. Comey, sent a letter to Congress saying an analysis of the emails found on former Representative Anthony D. Weiner’s laptop did not change the bureau’s decision from the summer that Mrs. Clinton should face no charges in the investigation of her emails.
That was the basic distillation of Mr. Comey’s new letter, saying that a review of the thousands of emails found on a laptop belonging to Mr. Weiner, the estranged husband of top Clinton aide Huma Abedin, would not lead to any new actions by the agency.
It was 10 days ago when Mr. Comey apprised Congress of the newly discovered emails, jolting the presidential race.
The letter injected the contest with a fresh level of skepticism about Mrs. Clinton that Democratic and Republican pollsters had reported seeing in surveys.
Mr. Trump initially described the renewed interest in the emails as bigger than the Watergate burglary.
Democrats responded to the original letter with fury and derision. How they handle the latest news, up and down the ticket, remains to be seen. But the new twist once again draws attention to a fraught topic for Mrs. Clinton. Early indications suggest that Democrats plan to continue pounding Mr. Comey for days to come.
Mr. Comey’s letter from Oct. 28 gave Mr. Trump new life after months of damaging fallout from the release of a recording from 2005 in which he boasted about committing sexual assault.
But on Sunday, in the wake of the latest F.B.I. news on the emails, Mr. Trump behaved as if nothing had changed.
Speaking in Minnesota just moments after the news broke, Mr. Trump delivered a speech asserting that Mrs. Clinton will probably see a criminal trial soon.
Sticking with facts has never been a deep preoccupation for Mr. Trump when trying to make a point.
And a number of his supporters are just as likely to believe that the F.B.I. caved under pressure, as Newt Gingrich, a Trump ally, suggested on Twitter. But the closing hours of the campaign are likely to widen the gap between facts and reality.
For months, the public reactions from Republican candidates and elected officials to their standard-bearer have ranged from a full-on embrace to outright disdain, to something in between.
In the final hours of the race, Republicans will be faced with a choice about what to say about a nominee who has often run against the party itself.
The House speaker, Representative Paul D. Ryan, put out a statement on Sunday after Mr. Comey’s letter, saying that electing Mr. Trump was still preferable to a second Clinton administration.
It was just a few weeks ago that Mr. Ryan indicated to members of his caucus that he would not continue defending Mr. Trump publicly.
But Mr. Trump continues to enjoy support among the party’s base, whose backing Republican candidates will need down the ballot. And so the dance has gone on.
Much has been made about Mrs. Clinton and Mr. Obama heading to Michigan, a state Mr. Trump’s aides believe they can win.
According to their estimates, Mrs. Clinton is less popular there than Mr. Obama was in 2012.
Mrs. Clinton is struggling with union households in states like Ohio, in a way that Mr. Obama did not in his 2012 re-election. Mrs. Clinton and Mr. Obama will also attend an all-star event in Philadelphia, where Bruce Springsteen, Jon Bon Jovi and Michelle Obama will appear.
Unions have been working hard to keep their members supporting Mrs. Clinton. So far, polls suggest, that has been a challenge.
But with Nevada and Pennsylvania appearing to lean in Mrs. Clinton’s favor, even if Mr. Trump wins North Carolina, Ohio and Florida, he would also have to win Michigan or Wisconsin to have a path to victory.