Hillary Clinton campaigned Friday in the company of friends and celebrities, first flanked by the billionaire businessman Mark Cuban in Pittsburgh and Detroit, and then at a concert in Cleveland with Jay Z and Beyoncé.
High-wattage political leaders fanned out for her around the country: Her husband, Bill, stumped in Colorado, as President Obama rallied voters in North Carolina.
By comparison, Donald J. Trump was a lonely figure.
In the final days of the presidential race, Mr. Trump’s political isolation has made for an unusual spectacle on the campaign trail — and perhaps a limiting factor in his dogged comeback bid.
When it comes to bolstering Mr. Trump, the Republican Party is not sending its best: As party leaders have disavowed him or declined to back his candidacy, Mr. Trump has been left instead with an eclectic group of backup players to aid him in his last dash for votes. Though polls show Mr. Trump drawing closer to Mrs. Clinton, the most prominent Republicans in key swing states still fear that his unpopularity may taint them by association.
Mr. Trump acknowledged the relative bareness of his events at a rally on Friday night: In defiant language, Mr. Trump hailed the size of the crowd packed into an arena in Hershey, Pa.
“By the way, I didn’t have to bring J. Lo or Jay Z — the only way she gets anybody,” he said. “ I am here all by myself. Just me — no guitar, no piano, no nothing.”
Campaigning in New Hampshire earlier on Friday, Mr. Trump did not appear with either Senator Kelly Ayotte, a Republican seeking re-election, or Chris Sununu, the Republican nominee for governor. Ms. Ayotte withdrew her endorsement of Mr. Trump last month, and Mr. Sununu has kept an awkward distance from Mr. Trump in his closely divided state.
But Mr. Sununu’s father, John H. Sununu, 77, a former governor known for his irascible temper, introduced Mr. Trump with a crude joke about the Clintons.
“Do you think Bill was referring to Hillary when he said, ‘I did not have sex with that woman?’” Mr. Sununu cracked, drawing laughter from the crowd.
Mrs. Clinton, in contrast, has sought to overwhelm the political map with popular advocates for her campaign, deploying them to reinforce her support in the biggest states that will decide the election. Her surrogates have matched their schedules to voting deadlines across the country: In Fayetteville, N.C., Mr. Obama implored voters to turn out and cast ballots before the end of early voting on Saturday, and read a letter from Grace Bell Hardison, a 100-year-old North Carolinian whom local Republican officials recently sought to disqualify from voting.
In every speech this week, Mr. Obama has told his crowd the address of a nearby polling place; in Fayetteville, he notified them that there was an early voting location across the street.
And Mr. Obama appealed for calm when a man waving a Trump sign briefly interrupted the event, drawings boos before the man was ushered out of the arena at Fayetteville State University.
Mr. Obama told the audience that the Trump supporter, who was wearing a beret and military-style coat with medals, deserved their respect because he appeared to be an older veteran.
“And don’t boo,” Mr. Obama said, as he was drowned out by thousands of people shouting “Vote!” in response.
Mrs. Clinton also had Vice President Joseph R. Biden Jr. campaigning in Wisconsin and Senator Bernie Sanders in Iowa on Friday. And after her appearance with Jay Z in Cleveland, Mrs. Clinton was due in Philadelphia on Saturday for a concert with Katy Perry and Stevie Wonder, and then back in Ohio with LeBron James, the Cleveland Cavaliers star. Her schedule culminates on Monday in what may be the biggest event of her campaign since the convention: an election-eve rally in the city with her husband, Mr. Obama and his wife, Michelle.
In Pittsburgh on Friday, Mrs. Clinton basked in the embrace of popular figures, including Mr. Cuban and a phalanx of former Pittsburgh Steelers: Walking onstage, she hailed “my two escorts, Mel Blount and Franco Harris,” both football Hall of Famers, and promoted the support of the Rooney family, which owns the team.
Mr. Cuban, the colorful owner of the Dallas Mavericks and a television personality, denounced Mr. Trump, telling voters the Republican nominee would sell them out for a check from Presidents Vladimir V. Putin of Russia or Bashar al-Assad of Syria.
“Do you think he cares more about you or his bank account?” Mr. Cuban asked the crowd. “Can you trust Donald Trump? Absolutely not.”
Advisers to Mr. Trump have argued publicly that he still has a path to victory in the race, while privately insisting to donors that they see new political opportunity in three states long seen as leaning toward Mrs. Clinton. They are particularly keen on Michigan, New Mexico and Nevada, according to Republicans briefed on their strategy, who spoke on the condition of anonymity.
But in each of those states, the best-known local Republicans have shunned Mr. Trump: The Republican governors of all three states have withheld their support, and Representative Joe Heck of Nevada, the Republican nominee for Senate there, withdrew his endorsement of Mr. Trump last month. (Mr. Heck has given indistinct signals since as to whether he will vote for Mr. Trump.) Though local elected officials and some members of Congress have campaigned with him, Mr. Trump has almost entirely lacked the political star power of a conventional campaign.
Mr. Trump’s surrogate operation took another blow on Friday with the conviction of two former associates of Gov. Chris Christie of New Jersey for engineering a plot to snarl traffic on the George Washington Bridge. Mr. Christie, a Trump ally who has been leading his presidential transition team, was scheduled to campaign for Mr. Trump in New Hampshire over the weekend.
Mrs. Clinton’s campaign quickly seized on the convictions to try to embarrass Mr. Trump. Wryly invoking one of Mr. Trump’s signature lines, John D. Podesta, the campaign chairman, told reporters that Mr. Trump ought to “start by draining his own swamp and asking Mr. Christie to resign as the head of his transition.”
And certain leaders on the right who have given Mr. Trump their nominal backing have steered clear of appearing with him in public — or even uttering his name. Senator Ted Cruz of Texas, a former rival of Mr. Trump who campaigned this week in Iowa with Gov. Mike Pence of Indiana, Mr. Trump’s running mate, praised Mr. Pence warmly but declined to mention Mr. Trump.
The House speaker, Paul D. Ryan, who has endorsed Mr. Trump but declined to campaign on his behalf, told a Wisconsin radio host on Friday that it was essential for Republicans to “come home” and vote for the party’s entire ticket. Mr. Ryan planned to campaign with Mr. Pence over the weekend in Wisconsin.
But while Mr. Ryan asked voters on Friday, forcefully and repeatedly, to support Senator Ron Johnson, the state’s embattled incumbent, he mentioned Mr. Trump only once and in passing.