WASHINGTON (AP) — Damaged but defiant, Donald Trump is limping toward a critical presidential debate against Hillary Clinton absent the backing of a growing group of Republican leaders. Trump insists he will "never" abandon his White House bid despite calls for him to step aside after his vulgar descriptions of sexual advances on women were revealed.

Trump's task in Sunday's faceoff is enormous, and perhaps insurmountable. Even before the recording of his remarks were made public, the businessman was lagging behind Clinton after an undisciplined first debate and struggling to overcome deep skepticism among women about his temperament and qualifications to be commander in chief.

Ohio Republican Party Chairman Matt Borges said that for Trump, "The debate is now everything."

Trump has hinted he may turn the debate into a referendum on Clinton's marriage, namely her husband's extramarital affairs and her treatment of the women who were involved. In what was billed as a videotaped apology for his actions, Trump said "Bill Clinton has actually abused women" and Hillary Clinton "bullied, attacked, shamed and intimidated" her husband's "victims."

Outside Trump's small cadre of advisers, support for the businessman was scarce following Friday's release of the 2005 videotape in which he can be heard detailing his attempts to have sex with a married woman. In an extraordinary rebuke, Trump's own running mate, Indiana Gov. Mike Pence, declared he could neither condone nor defend the remarks.

"We pray for his family," Pence said in a statement after canceling a Wisconsin appearance scheduled with House Speaker Paul Ryan and the Republican National Committee chairman, Reince Priebus, both of whom had condemned Trump's remarks but stopped short of withdrawing support altogether.

Several other Republicans did take the extraordinary step of revoking support for their party's nominee one month from Election Day and with early voting already underway in some key states.

Among them: Ohio Sen. Rob Portman, New Hampshire Sen. Kelly Ayotte — both are running for re-election — and the party's 2008 nominee, Arizona Sen. John McCain, who had stood by Trump even after the billionaire questioned whether the former POW should be considered a war hero because he got "captured."

McCain, who is also facing a challenge in November, said Trump's behavior made it "impossible to continue to offer even conditional support for his candidacy."

Many went further and called on Trump to quit the race altogether.

"I thought supporting the nominee was the best thing for our country and our party," Alabama Rep. Martha Roby said in a statement. "Now, it is abundantly clear that the best thing for our country and our party is for Trump to step aside and allow a responsible, respectable Republican to lead the ticket."

Republican leaders have scheduled a Monday morning conference call for House GOP lawmakers, who are out of town for Congress' election recess. The email obtained by The Associated Press doesn't specify the topic for the 11 a.m. EDT call, but rank-and-file lawmakers believe it's about Trump. Such calls are rare and usually held to discuss important matters.

Trump, who spent Saturday hunkered down in his New York skyscraper, tweeted that he would not yield the GOP nomination under any circumstances: "The media and establishment want me out of the race so badly - I WILL NEVER DROP OUT OF THE RACE, WILL NEVER LET MY SUPPORTERS DOWN!"

Indeed, many Trump voters remained loyal to the political outsider. Wisconsin voter Jean Stanley donned a shirt proclaiming "Wisconsin Women Love Trump" and called Ryan a "traitor" for denouncing the presidential contender's comments.

"He's a real human," Stanley said of the New York businessman, surrounded by Trump supporters at the Wisconsin rally where he was set to appear before the videotape emerged.

The political firestorm was sparked by a 2005 video obtained and released Friday by The Washington Post and NBC News. In the video, Trump, who was married to his current wife at the time, is heard describing attempts to have sex with a married woman. He also brags about women letting him kiss them and grab their genitals because he is famous.

"When you're a star they let you do it. You can do anything," Trump says in the video. He adds seconds later: "Grab them by the p----. You can do anything." He said of his impulse to kiss beautiful women: "I don't even wait."

While still publicly backing Trump, the Republican National Committee is considering how to move forward.

One possibility: re-directing its expansive political operation away from Trump and toward helping vulnerable Senate and House candidates. Such a move would leave Trump with virtually no political infrastructure in swing states to identify his supporters and ensure they vote.

"We are working to evaluate the appropriate messaging going forward," said RNC chief strategist Sean Spicer.

Election law experts suggest it would be logistically impossible to replace Trump on the ballot altogether, with early voting underway in some states and overseas ballots already distributed to military servicemen and others.

Ryan fundraising chief Spencer Zwick, however, said he's been fielding calls from donors who "want help putting money together to fund a new person to be the GOP nominee."

Zwick told the AP that a write-in or "sticker campaign" relying on social media could "actually work." While there has never been a winning write-in campaign in a U.S. presidential contest, such an effort could make it harder for Trump to win.

The release of the recording and ensuing backlash almost completely overshadowed the release of hacked emails from inside the Clinton campaign that revealed the contents of some of her previously secret paid speeches to Wall Street.

The Democratic nominee told bankers behind closed doors that she favored "open trade and open borders" and said Wall Street executives were best-positioned to help overhaul the U.S. financial sector. Such comments were distinctively at odds with her tough talk about trade and Wall Street during the primary campaign.

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Associated Press writers Jonathan Lemire and Jill Colvin in New York, Bill Barrow in Atlanta, Julie Bykowicz and Alan Fram in Washington, and Scott Bauer in Elkhorn, Wisconsin, contributed to this report.