By Chris Kahn

NEW YORK (Reuters) - Donald Trump has fallen further behind Hillary Clinton and now trails her by 8 points among likely voters, according to a new Reuters/Ipsos opinion poll, with 1 in 5 Republicans saying his vulgar comments about groping women disqualify him from the presidency.

The national tracking poll was launched after Sunday night's second presidential debate, where Trump was pressed to explain his comments in a 2005 videotape about grabbing women's genitalia. He described the remarks, which first surfaced on Friday, as "locker room" banter and apologized to Americans.

The poll released on Tuesday showed Clinton, the Democratic nominee, had increased her lead over Trump, the Republican nominee, to 8 percentage points on Monday from 5 points last week.

When asked to pick between the two major-party candidates, 45 percent of likely voters said they supported Clinton while 37 percent supported Trump. Another 18 percent said they would not support either candidate.

Trump was under pressure during Sunday's debate to restore confidence in his struggling campaign after dozens of lawmakers repudiated him over the weekend. He hammered Clinton's handling of classified information while serving as secretary of state and referred to her as "the devil." At one point, he said he would jail Clinton if he were president.

Among those who said they watched at least portions of the debate, 53 percent said Clinton won while 32 percent said Trump won. The results fell along partisan lines, however: 82 percent of Democrats felt Clinton won, while 68 percent of Republicans felt that Trump won.

Among likely voters who watched the debate, 48 percent said they supported Clinton while 38 percent supported Trump.

'LOCKER ROOM TALK'

In the 2005 Access Hollywood video Trump boasted about making unwanted sexual advances toward women. "When you’re a star they let you do it," he is heard saying.

Some 61 percent of those polled said that "lots of men" occasionally engage in similar conversations, and 46 percent, a plurality, said it was unfair to judge someone on conversations "that they did not intend for anyone else to hear."

Most of those polled said they believe Trump is a sexist, but they were split on whether his comments disqualify him from being president. Some 42 percent of American adults, including 19 percent of registered Republicans, said Trump's comments disqualified him, while 43 percent said they did not.

Among Republicans, 58 percent said they want Trump to remain atop their party's ticket, and 68 percent said the Republican leadership should stand by him.

The video doesn't appear to have worsened Trump's standing among women, who mostly had a low opinion of him already, according to Reuters/Ipsos polling over the past 12 months.

When asked to pick between the two candidates, about 44 percent of women chose Clinton while 29 percent selected Trump - roughly the same proportion as measured in polls conducted before the weekend.

Trump, however, appears to be shedding support among evangelicals, who are usually a wellspring of support for Republican presidential candidates. Monday's poll showed that Trump had only a 1-point edge over Clinton among people who identified as evangelicals. That’s down from a 12-point advantage for Trump in July.

The Reuters/Ipsos poll is conducted online in English in all 50 states. The poll of 2,386 American adults included 1,839 people who watched the debates, 1,605 people who were considered likely voters due to their registration status, voting history and stated intention to vote in the election. Among the likely voters, the poll counted 798 Democrats and 586 Republicans.

The poll has a credibility interval, a measure of accuracy, of 2 percentage points for the entire group, 3 points for likely voters and the debate watchers, 4 points for Democrats and 5 points for Republicans.

National opinion polls have measured support for the candidates in different ways this year, yet most agree that Clinton is leading and that her advantage has strengthened as the general election approaches.

RealClearPolitics, which tracks most major opinion polls, shows Clinton ahead of Trump by an average of 7 percentage points, and that her lead has grown since the middle of September.

(Reporting by Chris Kahn, editing by Ross Colvin)