Mr. Trump’s campaign reeled over the weekend after the Friday release of a video recording that showed him speaking in vulgar and demeaning terms about women and boasting of how, because he was a celebrity, he could grope and kiss them whenever he wanted. Despite tepid apologies, the revelation has led to a parade of denouncements from dozens of Republican leaders, including his running mate, Gov. Mike Pence of Indiana.
Mr. Trump continued to push back against calls from Republicans to quit the race, mocking them on Twitter and directing his loyalists to assail the party’s leaders as politicians guided by self-interest.
He also signaled on Sunday that he was likely to make the behavior of former President Bill Clinton an issue in the debate.
Trump escalates confrontation that could hurt the G.O.P. in November.
In a set of talking points sent to supporters on Sunday morning, Mr. Trump instructed his backers to attack Republican leaders — and vowed to win without them.
“A lot of the people who are being so critical now are the same ones who doubted him before,” read the talking points, which were forwarded by a Republican strategist. “They are more concerned with their political future than they are about the future of the country. Mr. Trump won the Primary without the help of the insiders and he’ll win the General without them, too.”
Mr. Trump amplified the email, taking to Twitter on Sunday to lash out at critics within the party at the very moment some of them are pressing him to show contrition.
“So many self-righteous hypocrites,” he wrote of the Republicans who rescinded their support. “Watch their poll numbers — and elections — go down!”
President Obama weighs in on Trump’s comments.
“One of the most disturbing things about this election is just the unbelievable rhetoric coming from the top of the Republican ticket,” Mr. Obama said at an afternoon fund-raiser in Chicago. “I don’t need to repeat it. There are children in the room.”
But he cited a litany of Mr. Trump’s comments including those that are “demeaning and degrading women,” “mocking the disabled” and “insulting our troops.”
“That tells you he’s insecure enough that he pumps himself up by putting other people down,” Mr. Obama said.
Cruz criticizes NBC, but hasn’t walked away from Trump.
It was just two weeks before Mr. Trump’s lewd recording was released that Senator Ted Cruz finally broke down and endorsed the Republican nominee.
Putting aside their policy differences and the fact that Mr. Trump disparaged Mr. Cruz’s wife and father during their primary battle, Mr. Cruz said that after considerable thought and prayer he had concluded that Mr. Trump would make a better president than Hillary Clinton.
As scores of Republican leaders rescinded their support for Mr. Trump this weekend, Mr. Cruz said he was still deciding what to do about his endorsement.
In the meantime, Mr. Cruz took to Twitter on Sunday to criticize the news media for failing to uncover such damning material about Mr. Trump sooner.
“NBC had tape 11 yrs,” Mr. Cruz wrote, accusing the mainstream news media of bias. “Apprentice producer says they have more & worse. So why not release in 2015? In March?”
Here are a few of the other things we’ll watch for in Sunday’s face-off:
How — and how quickly — will Trump apologize during the debate?
Rudolph W. Giuliani, the former New York City mayor who is a top adviser to Mr. Trump, said on ABC News on Sunday that he expected Mr. Trump to apologize during the debate and make the case that he is a changed man. Mr. Giuliani called Mr. Trump’s remarks on the tape “horrible” and “reprehensible,” and he expressed hope that Mr. Trump’s suggestions in the recording that he assaults women were exaggerated.
“He’s very embarrassed and contrite about it,” Mr. Giuliani said. “There is no excuse or answer for it, other than ‘I’m very sorry and I wish I hadn’t done it and I’m not like that any more.’”
Will Trump go nuclear?
While some strategists have suggested that Mr. Trump should strike a humble tone at the debate, many are bracing for the tenor to become even nastier.
Surrogates for Mr. Trump, and the candidate himself, have been busy comparing what he said on camera in 2005 to Mr. Clinton’s indiscretions with women. On Saturday night, Mr. Trump shared Twitter posts from an account that says it belongs to Juanita Broaddrick, who long ago accusedBill Clinton of rape. On Sunday Mr. Trump posted a Breitbart.com articleon Twitter that features an interview with Ms. Broaddrick.
Mr. Trump has been threatening for weeks that he would force Mrs. Clinton to respond directly to old allegations of harassment and assault against her husband in front of a national audience of tens of millions of people.
The temptation is obvious. Mr. Trump is clearly enraged by news media coverage of his own offensive and inappropriate behavior, and believes that hypocrisy and special treatment have deflected attention from Mr. Clinton.
But so are the risks. Polling suggests that a majority of voters aren’t that interested in hearing more about Mr. Clinton’s behavior. And Mr. Clinton isn’t running for president — Mrs. Clinton is.
Who will wow the crowd?
The format for the debate, in St. Louis, is town hall-style, with an audience of voters who will ask their own questions of the candidates. Mrs. Clinton has extensive experience with the format. Some of her best and freshest campaign moments have come when she is not behind a lectern.
But so was one of her worst: the commander-in-chief forum in September, when the moderator, Matt Lauer, and the questioners in the audience hammered Mrs. Clinton over her violation of email security protocols at the State Department. But Mr. Trump’s preferred venue is the raucous rally, where he alone has the microphone.
Town halls can be treacherous in ways typical debates are not. The candidates have to interact directly with voters in the audience, showing them respect, paying attention to their questions and seeking a direct connection that is obvious to viewers at home. Mrs. Clinton is practiced at these maneuvers. Mr. Trump has a tendency to disappear into his own verbal fog, to ignore the question entirely and to fail to give an actual answer.
And if an audience member drills into sensitive territory — such as the 2005 recording — there is always the danger of an explosive and dismissive response.
Will Clinton control the debate again?
What emerged over the course of the first debate was evidence of Mrs. Clinton’s deep preparation for the encounter. Within 20 minutes, she had taken full control of the rhythm of the debate, pulling Mr. Trump into an array of damaging exchanges: over his responsibility for discredited “birther” theories about President Obama; his avoidance of taxes; and most spectacularly, his shaming of a former Miss Universe contestant named Alicia Machado over her weight. Each time, he took the bait.
Mrs. Clinton will no doubt arrive in St. Louis equipped with a fresh pail of chum to throw in the waters around Mr. Trump, determined to whip him into a frenzy. She will needle him over revelations of the scale of his tax avoidance. She will cite the array of attacks on him from his own party this weekend. To achieve anything resembling a victory, Mr. Trump will need to turn up his nose and focus on the most compelling parts of his own message: trade, the threat of Islamic militants, and the creation of jobs.
And here’s how to watch the debate.
■ Start time: 9 p.m. Eastern
■ Duration: About 90 minutes
■ Moderators: Martha Raddatz of ABC, and Anderson Cooper of CNN
■ Airing on TV: ABC, CBS, CNN, Fox, Fox Business Network, Fox News, MSNBC and others.
■ Streaming online: We think nytimes.com is a pretty good place to turn to.