The Republican nominee, in a shocking video released by The Washington Post Friday, was caught using vulgar language about groping and kissing women with impunity.
"I've said and done things I regret," he said in a televised apology, believed to be the first of his 16-month White House campaign.
"Anyone who knows me knows these words don't reflect who I am. I said it, I was wrong, and I apologize."
Trump was facing savage criticism after release of the video, which landed like a bombshell and gave his Democratic rival Hillary Clinton fresh ammunition to attack his misogyny as they prepared for their second presidential debate, on Sunday in St. Louis.
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"I've never said I'm a perfect person, nor pretended to be someone I'm not," Trump said.
"I pledge to be a better man tomorrow."
Damage not controlled
But major damage was already done, with several fellow Republicans withdrawing their endorsements of Trump.
"I can no longer in good conscience endorse this person for president," Republican congressman Jason Chaffetz of Utah told Fox.
"It is some of the most abhorrent and offensive comments that you can possibly imagine."
Other Republicans reportedly including congresswoman Barbara Comstock, congressman Mike Coffman and former Utah governor Jon Huntsman, who ran for president in 2012, demanded Trump exit the race.
In the video from 2005, obtained and released by The Washington Post, Trump uses extraordinarily vulgar and predatory language as he describes hitting on a married woman and grabbing women's crotches.
"When you're a star they let you do it. You can do anything," he is heard saying.
Trump finds himself mired in fresh scandal at a crucial point in the campaign with just one month until Election Day on November 8 and Clinton expanding her lead in national and battleground state polling.
Clinton is seeking to become the nation's first female commander in chief, and the former secretary of state is almost certain to call out Trump over the troubling video footage in their prime-time Sunday showdown.
Trump's coarse language, shocking even by the standards of this year's campaign, comes at a make-or-break moment for Trump, as he trails his Democratic rival in national polls and women, furious over his series of demeaning comments, are seen overwhelmingly backing Clinton.
'Sickened'
The three-minute video captures Trump reacting to an actress he was about to meet as he arrived on the set of daytime soap opera "Days of Our Lives," for a taping of a segment in which he was to have a cameo appearance, the Post said.
"I've gotta use some Tic Tacs (breath mints), just in case I start kissing her," Trump says to Billy Bush, then host of the "Access Hollywood" show about celebrities.
"You know I'm automatically attracted to beautiful. I just start kissing them. It's like a magnet," he says.
"I don't even wait. And when you're a star they let you do it. You can do anything."
Trump also is heard bragging about trying to have sex with a married woman.
"I moved on her and I failed. I'll admit it," the billionaire Trump tells Bush, using an expletive for how he tried to have sex with her.
"I moved on her like a bitch, but I couldn't get there. And she was married," Trump says.
The tape was recorded months after Trump married his third wife, Melania, according to the Post.
House Speaker Paul Ryan, the nation's top elected Republican, led a chorus of party criticism of their flagbearer.
"I am sickened by what I heard today. Women are to be championed and revered, not objectified," Ryan said, adding that Trump was disinvited from a political event Saturday in Wisconsin.
File image of House Speaker Paul Ryan. Source: AAP
Trump's campaign then said his running mate Mike Pence would be attending the event instead, while Trump would prepare for his debate.
With Team Trump in damage control, he issued a rare apology.
But the provocative billionaire quickly and defiantly pivoted from his own crisis to attack former president Bill Clinton, saying Hillary's husband "abused" women.
"Bill Clinton has actually abused women, and Hillary has bullied, attacked, and shamed his victims.
"We'll discuss this in the coming days," Trump said. "See you at the debate on Sunday."
Clinton strongly condemned Trump's comments.
"This is horrific. We cannot allow this man to become president," she posted on Twitter.
Republican National Committee chairman Reince Priebus, a longtime Trump defender, and several Republican US senators, including 2008 presidential nominee John McCain, lit into Trump.
"He alone bears the burden of his conduct and alone should suffer the consequences," McCain said.
The question is how Trump bounces back from the most serious crisis of his campaign.
The Republican nominee is already in trouble with women voters. Experts say Trump would need to make inroads with white women voters if he were to be able to make up ground against Clinton in the coming weeks.
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