WASHINGTON (Reuters) - Republican presidential nominee Donald Trump, facing eroding support from his party over lewd remarks about women, goes into a second presidential debate with Democrat Hillary Clinton on Sunday needing to demonstrate he remains a credible candidate.

Republican presidential nominee Donald Trump waves to supporters outside the front door of Trump Tower where he lives in the Manhattan borough of New York, U.S., October 8, 2016. REUTERS/Mike Segar

The pressure on the 70-year-old Trump at the debate will be intense. Not only must he parry attacks from Clinton and explain why he is a better alternative. He must also show an apologetic side to stop more Republican supporters from giving up on him.

Trump already had an uphill battle to win the White House in the Nov. 8 election before disclosure of a 2005 video in which he could be heard talking crudely about women.

A Reuters-Ipsos poll had Clinton leading by five points on Friday, before the video surfaced. Now, the question is whether Trump’s quest for the presidency is all but over.

The fresh controversy adds an air of unpredictability over the 9 p.m. EDT debate at Washington University in St. Louis, the second of three scheduled presidential debates as the long-running U.S. election contest enters its final weeks.

It will be a town hall-style debate with undecided voters posing half the questions and the debate’s two moderators posing the others.

His vice presidential running mate, Mike Pence, said on Sunday that Trump needs to show contrition.

“We pray for his family and look forward to the opportunity to show what is in his heart when he goes before the nation tomorrow night,” Pence said in a statement.

The crisis has put the Republican National Committee in a tight spot with less than a month to go until Election Day.

Trump would have to resign the nomination to allow Republican leaders to choose a successor, but the New York businessman is showing no signs of stepping down despite increasing calls from elected leaders for him to let Pence become the nominee.

“The media and establishment want me out of the race so badly - I WILL NEVER DROP OUT OF THE RACE, WILL NEVER LET MY SUPPORTERS DOWN!” Trump tweeted on Sunday from Trump Tower in New York.

At the first debate, on Sept. 26, Trump was repeatedly put on the defensive by Clinton. He never let her accusations go unanswered, and as a result he missed opportunities to use his speaking time to draw attention to Clinton’s perceived weaknesses.

Republicans said Trump needed to perform more like Pence, who was deemed the winner in his vice presidential debate against Democratic rival Tim Kaine last week.

Republican strategist Ron Bonjean said there is plenty Trump could learn from Pence, who stayed on offense at the vice-presidential debate, did not bother to respond to Kaine’s accusations, and looked calm and unflappable.

“It was a clear lesson in how you avoid falling into your opponent’s traps,” Bonjean said. “Don’t talk about what the other side wants you to talk about, focus on what you want to talk about.”

Clinton has been hunkered down for days getting ready for what could be, for her, a knockout blow against Trump.

Before the video surfaced, Clinton campaign officials said they were expecting the Republican nominee to come to the debate more subdued than the first round.

But they were also prepared in case Trump follows through with a threat to focus on Clinton’s sometimes troubled marriage to former President Bill Clinton.

Clinton, who has already capitalized on Trump’s treatment of women, herself foreshadowed how she might respond to an attack from Trump on her marriage during a speech to a fundraiser in Washington on Wednesday.

“I feel it’s my responsibility not to defend myself against his attacks because, really, been there, done that,” she said. “I think it’s my responsibility to defend everybody else against his attacks,” she said, drawing cheers from the crowd.

Clinton has her own issues to face. Wikileaks on Friday published an email from Clinton advisers appearing to contain excerpts of paid speeches to corporations, in which Clinton voices support for open trade and borders and says how sometimes it is important to have a public and private position.