WASHINGTON/ST. LOUIS (Reuters) - The U.S. Republican Party on Sunday confronted its biggest crisis in more than 40 years when its presidential nominee, Donald Trump, faced a storm over sexually aggressive comments he made about women in a newly uncovered 2005 video.

Only a month before the Nov. 8 election and on a day when Trump was due to debate Democratic presidential nominee Hillary Clinton, Trump took to social media to squelch any speculation that he would leave the race.

“Tremendous support (except for some Republican leadership”). Thank you,” Trump wrote on Twitter.

Then in a last-minute surprise in St. Louis, host city for the town-hall debate, Trump called journalists into a hotel room to witness a meeting he held with four women who revived accusations of past sexual misdeeds by Clinton’s husband, former President Bill Clinton.

The party turmoil recalled past party crises, including the Watergate scandal that led to Republican President Richard Nixon’s resignation in 1974.

A businessman-turned-politician previously best known to Americans as a reality TV show host, Trump, 70, faced his latest crisis when on Friday the 2005 video emerged in which he was heard talking on an open microphone about groping women and trying to seduce a married woman. The video was taped only months after Trump married his third wife, Melania.

The controversy pitched Trump, 70, into the biggest crisis of his 16-month-old campaign and deepened fissures between him and establishment Republicans. On Sunday, he struck a defiant tone in the face of calls for him to abandon the race.

A source close to the campaign of Trump’s vice presidential running mate, Mike Pence, dismissed talk among some political analysts the Indiana governor might bolt the ticket in the uproar over Trump’s comments.

“Absolutely not,” the source told Reuters.

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At a Democratic campaign event in Chicago, President Barack Obama weighed in on the controversy, saying Trump had been degrading not only to women, but to minorities, immigrants, people of other faiths, and the disabled.

Obama said that “tells you he is insecure.”

“He pumps himself up by putting other people down,” Obama said.

SUPPORT WOBBLING

With Republican Party leaders in crisis mode and doubts emerging over Trump’s ability to draw support from crucial undecided voters, there were nonetheless some early signs many of his core supporters would remain loyal.

A public opinion poll by POLITICO/Morning Consult, taken just after news broke of the video, found 39 percent of voters thought Trump should withdraw, and 45 percent said he should stay. Of those who said Trump should leave, only 12 percent identified themselves as Republicans.

As of Sunday afternoon, at least 160 of the United States’ 332 sitting Republican governors, senators and House of Representatives members had condemned Trump’s remarks, according to a Reuters review of official statements and local news coverage.

At least 30 had called for him to withdraw from the race and three other officeholders said he should consider doing so. Eight of those said they were withdrawing their endorsement as well.

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Those facing a difficult re-election were more likely to speak out. All but six of the 40 Republican officeholders whose races are considered competitive had condemned Trump’s comments on the video, although only three members of that group called for him to drop out.

Any attempt to replace Trump on the ballot would face huge legal and logistical hurdles.

The Trump campaign was battling back, circulating “talking points” to a core of high-profile Republicans who promote Trump in the news media. The points sought to undermine establishment Republicans who have abandoned Trump.

“They are more concerned with their political future than they are about the future of the country,” said a copy of the talking points, described to Reuters by two sources close to the campaign.

A real estate developer making his first run at public office, Trump has made his battle against the establishment a central campaign theme.

“Phones have been blowing up for the past 24 hours,” said a prominent Republican political operative in Washington, referring to a heavy volume of calls among party officials and Republican members of Congress.

DOWN-BALLOT RACES

The operative, who did not want to be identified, said Trump’s troubles could steer campaign donations away from him and to Republican candidates for Congress and other down-ballot offices.

The source said Trump could help himself most during the presidential debate - the second of three before the election - if he addressed the video and an Oct. 1 New York Times report that he took so substantial a tax deduction on a declared $916 million loss in 1995 that he could legally have avoided paying any federal income taxes for up to 18 years.

Despite having recovered from a string of setbacks, Trump had an uphill battle to win the White House. Before the video surfaced, a Reuters/Ipsos poll had Clinton leading by 5 points on Friday. The question now is whether Trump’s quest for the presidency has been dealt a lethal blow.