One of the conservatives, Representative Dana Rohrabacher of California, attacked the Republicans stepping away from Mr. Trump as âcowards,â three lawmakers said. Another, Representative Trent Franks of Arizona, said, using graphic language to describe abortion, that allowing Mrs. Clinton into the White House would end with fetuses being destroyed âlimb from limb.â
Trying to quiet the uproar, Mr. Ryan interjected after about 45 minutes to assure members that he was not withdrawing his endorsement of Mr. Trump, but rather doing what he felt was in the best interests of the House.
For five months, Mr. Ryan and Mr. Trump have alternated between friction and courtship, eventually forging an uneasy working relationship only to see it collapse now, in the final weeks of the race.
AshLee Strong, a spokeswoman for Mr. Ryan, confirmed that his sole priority for the remainder of the election would be defending congressional Republicans. âThe speaker is going to spend the next month focused entirely on protecting our congressional majorities,â she said.
Great Clash: Donald Trump vs. Paul Ryan
Mr. Trump did not repeat his Twitter jab at Mr. Ryan at a campaign event in Pennsylvania Monday afternoon, offering instead a red-meat diatribe unlikely to appeal beyond his dedicated base. He repeated his call from Sunday nightâs debate for a special prosecutor to pursue Mrs. Clinton, called her âthe devilâ and warned that her election would lead to âthe destruction of our country.â
A buoyant Mrs. Clinton seemed to revel in her growing advantage over Mr. Trump during a speech in Detroit on Monday afternoon. Mr. Trump, she said, had spent their debate âattacking when he should have been apologizing.â
While Mrs. Clinton made no direct reference to the fissures appearing among Republicans, her campaign tried to exploit the moment, releasing several television ads featuring voters who describe themselves as Republicans but plan to vote for Mrs. Clinton.
Jennifer Palmieri, Mrs. Clintonâs communications director, expressed little sympathy for Republicans now fleeing Mr. Trump.
âThere was a time when they could have spoken out against him,â Ms. Palmieri said of party leaders like Mr. Ryan. âThat time was this summer. Obviously, it is too late now.â
Graphic: More Than 160 Republican Leaders Donât Support Donald Trump. Hereâs When They Reached Their Breaking Point.
The consequences for both men are enormous. Mr. Ryan and other Republican leaders fear that Mr. Trumpâs flagging campaign will imperil their majorities in the House and Senate, and Mr. Trump can ill afford more prominent rejections when he is trying to rally reluctant Republican voters behind him.
Mr. Trumpâs candidacy was already in dire condition before Mr. Ryanâs announcement. A poll published Monday by NBC News and The Wall Street Journal found him trailing Mrs. Clinton by a wide margin, drawing less than 40 percent of the vote. The survey was taken before the debate.
And in a sign of how deep divisions now run among Republicans, the chairman of the Republican National Committee, Reince Priebus, held a conference call of his own after Mr. Ryanâs to emphasize his commitment to Mr. Trump. Mr. Priebus told members that the committee was working in âfull coordinationâ with the Trump campaign and planned to direct âa lotâ of money to the presidential race.
âNothing has changed in our support for our nominee,â he said, vowing âan incredible four weeksâ until the election.
Mr. Priebus, long a close political ally of Mr. Ryan, made no direct reference to the speakerâs announcement, or to the dozens of governors and members of Congress who have rescinded their support for Mr. Trump.
Credit Doug Mills/The New York Times
Representative Scott Rigell of Virginia, a Republican who has long opposed Mr. Trump, said there was a general sense in the House that more humiliating disclosures about Mr. Trump were likely to come before Nov. 8, Election Day.
âThereâs a consensus, even among supporters, that the likelihood of something else breaking in a very embarrassing and negative fashion is certainly better than 50-50,â said Mr. Rigell, who joined the call on Monday. âThe conference, members, et cetera, are bracing themselves for another salvo of this.â
Mr. Trump seemed to acknowledge that possibility in Pennsylvania, commenting offhand in his speech that if more recordings were to emerge, he would respond with more personal attacks on Mrs. Clinton and her husband.
Mr. Trumpâs allies had hoped that the debate would halt the exodus of fellow Republicans from his candidacy, and they publicly implored members of the party on Monday to stick with him through Election Day. Gov. Mike Pence of Indiana, Mr. Trumpâs running mate, punctured speculation that he might withdraw from the race by pronouncing himself âproud to stand with Donald Trumpâ in a visit to North Carolina.
Kellyanne Conway, Mr. Trumpâs campaign manager, also offered an ominous warning for Republicans fleeing Mr. Trump. She noted on television that Mr. Ryan had been booed by Trump fans over the weekend in Wisconsin and said she knew of Republican lawmakers who had behaved inappropriately toward young women, and whose criticism of Mr. Trump was therefore hypocritical.
Just as telling as the frustration from outspoken conservatives in the House on Monday was the silence from so many mainstream Republicans in the chamber, who showed little appetite to argue for or with their embattled nominee.
Few anti-Trump voices weighed in on the call with Mr. Ryan. Representative Martha Roby of Alabama, who defected from Mr. Trump on Saturday, said she would contribute significant money to help Republicans hold their House majority. But she also said she would speak with colleagues in private about her decision to withdraw her endorsement in the presidential race.
Representative Charlie Dent of Pennsylvania, a vocal critic of Mr. Trump, asked his colleagues if they were truly confident that there would be no more damaging disclosures. In any case, Mr. Dent argued that the race was effectively over for Mr. Trump.
No new prominent Republicans have withdrawn their endorsements since the debate, but there was a palpable fear throughout the party that Mr. Trump had been damaged beyond repair.
Representative Greg Walden of Oregon, chairman of the National Republican Congressional Committee, urged members on the conference call to take polls in their districts to gauge the effect of Mr. Trumpâs political slide.
Credit Mandel Ngan/Agence France-Presse â Getty Images
Mr. Walden said they should brace for a significant erosion of support for Mr. Trump and acknowledged that the shift could hurt congressional candidates, too. He asked the entire caucus to contribute quickly to the partyâs campaign arm, making it clear that they needed to strengthen their defenses across the country.
At a briefing for Washington lobbyists later in the day, Mr. Walden acknowledged to donors that Republicans were in uncharted territory and wholly uncertain of what would happen next.
Still, many members were pointed in expressing their dismay to Mr. Ryan, warning him of grave consequences, in November and beyond, if Mr. Trumpâs campaign collapses altogether.
Representative Billy Long of Missouri spoke up in Mr. Trumpâs defense, citing the danger of losing the Supreme Court if Mrs. Clinton wins.
âMany of us commented that if Hillary picks the next two to four judges, it will change the fabric of our country of 40, 50 years,â Mr. Long said later. âAbortion and the Second Amendment, also, and lots of Supreme Court concerns.â
An earlier version of this article misstated the number of women Donald J. Trump held a news conference with to accuse Bill Clinton of sexual misdeeds. It was three, not four. A fourth woman at the event criticized Hillary Clinton for providing legal representation for a man accused of raping a child.