WASHINGTON: White House candidate Donald Trump desperately needs a strong debate performance against Hillary Clinton on Sunday, but a damaging video of him making lewd comments about women raises the stakes significantly.

His anything-but-ordinary presidential bid, and the embattled Republican Party with it, was thrown into disarray by the misogynistic comments, with growing calls from top Republicans for him to step aside.

Even before the latest fallout, Trump was already in need of a moment of political magic to reverse his slid in the polls barely four weeks from Election Day on November 8.

At 9:00 pm (0200 GMT Monday), the real estate magnate and the former secretary of state will face off in the second presidential debate at Washington University in St Louis.

The format poses its own difficulties for Trump: Half of the questions will be asked by undecided voters.

He will want to build a personal connection with these everyday Americans and show his capacity for empathy, a quality that often has been drowned out in his large, raucous campaign rallies.

Despite an angry backlash threatening to destroy his campaign, over Trump's remarks boasting about his ability to grope women as he pleases without impunity, he insisted there is "zero chance I'll quit."

Late Saturday, the defiant Republican presidential nominee stepped outside of his Trump Tower skyscraper in New York, brandishing his fist to cheers from dozens of supporters.

Asked if he was staying in the race, he responded: "100 percent."

Trump's own wife Melania said she was offended by her husband's "unacceptable and offensive" comments, caught on a hot mic just months after the two married in the real estate magnate's third marriage.

But she urged American voters to support him.

"I hope people will accept his apology, as I have, and focus on the important issues facing our nation and the world," Melania Trump said in a statement.

The videotape, released Friday by The Washington Post, forced a rare apology from a campaign already peppered by controversies over Trump's treatment of women, roiling his Republican Party.

The Republican National Committee appeared to have halted part of its "Victory" program to elect Trump, with the RNC asking a vendor to "put a hold" on mail production, the Politico news website reported.

CNN said the RNC was considering ending a joint fundraising agreement with the Trump campaign.

Trump called the disclosure a "distraction," defiantly attacking the Clintons for husband Bill Clinton's past infidelities, and hinting strongly he would say more on the topic during Sunday's debate in St Louis, Missouri.

Campaign in crisis

With the November 8 elections one month away and Clinton leading in the polls by nearly five percentage points nationally, the latest uproar has plunged Trump in the deepest crisis of his turbulent campaign.

He had already been seriously hurt by a sloppy performance in his first debate with Clinton on September 26, a damaging Twitter war against a former Miss Universe and reports he may have paid no income taxes for 18 years.

Clinton, who is seeking to become the nation's first female commander-in-chief, is almost certain to call out Trump about the videotape during the debate.

"This is horrific," she said on Twitter. "We cannot allow this man to become president."

In the video, Trump uses vulgar and predatory language as he describes hitting on a married woman and grabbing women's crotches.