Donald Trump will face Hillary Clinton in the second televised debate tonight, with his campaign in renewed crisis over "horrific" comments he made about women.
The Republican presidential candidate has faced a wave of criticism following the broadcast of a video from 2005 - but insisted he will "never withdraw" from the race for the White House.
The billionaire was recorded describing his attempt to seduce a married woman and boasting in vulgar terms of what he can do to women as a "star".
He cancelled a planned appearance in Wisconsin on Saturday after an invitation by House Speaker Paul Ryan was withdrawn as a result of the controversy.
Mr Ryan said he was "sickened" by the tycoon's comments.
In a video statement, Mr Trump promised to be a "better man". He said: "Anyone who knows me knows these words don't reflect who I am. I said it, I was wrong and I apologise."
But senior Republicans, including former California governor Arnold Schwarzenegger and Senator John McCain, have distanced themselves from the candidate.
Mrs Clinton, his Democratic rival, tweeted that the remarks were "horrific".
New GOP nominee?
Mr Ryan's fundraising chief Spencer Zwick said he had been fielding calls from donors who "want help putting money together to fund a new person to be the GOP nominee".
Mr Trump's wife, Melania, who he had recently married him at the time of the recording, has described her husband's comments as "unacceptable and offensive", but said she had accepted his apology.
The tycoon's running mate, Mike Pence, who many Republicans have said should now be the party's nominee, also put out a statement saying he could not condone or defend the remarks.
Mr Trump's history of comments about women were a feature of the first televised debate.
Mrs Clinton was judged to have won the debate and has subsequently seen a surge in opinion polls.
And in swing states like Colorado, Mr Trump is suffering among women voters in particular.
Female voters in Jefferson County near Denver have become a pivotal bloc in presidential elections.
"I think that women are terrified at what is being openly discussed and how they are being treated and talked about," said Brittany Pettersen, who represents the area in Colorado's House of Representatives.
"I have never seen anything like this before and I think that women are absolutely very concerned."
"Equal opportunities offender"
Shawna Fritzler was a registered Republican for 25 years but gave up her affiliation this summer.
She said: "My 11-year-old daughter said to me: 'We're Republicans, right? Please, no matter what you do, please tell me you're not going to vote for Trump'.
"I realised that by staying affiliated with the party, that was showing so much hate. I didn't want that label attached to me."
Her friend, Democrat-registered Jonna Levine, added: "I'd like to think that women are tired of being measured by what they wear, how much they weigh."
But members of Colorado Women for Trump dismissed questions about his attitude to women.
Charlene Hardcastle said: "He's an equal opportunities offender, he's non-PC and that's what I love about him. Americans are afraid to say what they really think."
Loretta Perry added: "He's not a polished speaker, he's not a politician. He's done some wonderful things for lots of women, there's nobody perfect on this earth."
Meanwhile, British interim UKIP leader Nigel Farage has waded into the crisis, insisting Mr Trump's remarks amounted to "alpha male boasting".
