Donald Trump

House of Representatives Speaker Paul Ryan vowed to focus on defending seats in Congress, but did not end his endorsement of the party's nominee.

Mr Trump tweeted that Mr Ryan should not waste his time fighting him.

Earlier Democratic rival Hillary Clinton cast doubt on Mr Trump's apology for the remarks, made 11 years ago.

On Sunday, Mr Trump described his words as "locker-room talk".

"If I win, I am going to instruct my attorney general to get a special prosecutor to look into your (missing email) situation," Trump said, "because there has never been so many lies, so much deception."

Trump's threat -- which he has made before on the campaign trail -- is extraordinary even by the standard of the vitriolic 2016 campaign.

On Friday, previously unaired 2005 footage revealed the Republican presidential nominee bragging about trying to have sex with a married woman and being able to grope women.

"When you're a star, they let you do it. You can do anything ... Grab them by the pussy. You can do anything," Trump had said.

Trump later issued a apology, calling the conversation "locker room banter."

Here's a look at all the times he called it "locker room" talk that during the debate:

1. 'This was locker room talk'

Trump's campaign was in free fall when he entered the debate hall Sunday night, reeling from the revelation of a 2005 video in which he spoke of women in lewd and sexually aggressive terms. The video sparked a dramatic rebuke of Trump, with dozens of Republicans in Washington and around the country saying the billionaire should step aside and let his running mate, Indiana Gov. Mike Pence, lead the GOP ticket.

The icy tone was set early when decades of tradition eroded as Trump and Clinton declined to shake each other's hand.

"My name is Arianne (R-E-on) ZUCKER (Zooker) and I am a strong, independent, hard working mother, business woman and partner to a great man. I have grown to learn that the words of others cannot effect the value of my self worth or define the content of my character," Zucker wrote.

Trump was talking with Bush on a bus outside of the soap opera "Days of Our Lives," and the pair noticed Zucker, who was waiting to escort them onto the set.

"I've got to use some Tic Tacs, just in case I start kissing her," Trump said.

The women were Paula Jones, who has accused Bill Clinton of propositioning her and exposing himself; Juanita Broaddrick, who claims Clinton sexually assaulted her; Kathy Shelton, who says Hillary Clinton defended a man who victimized her; and Kathleen Willey, who claims Bill Clinton groped her.

All four are expected to be in the audience tonight.

At least a dozen Republicans have said they will not be voting for him, since the comments emerged on Friday.

Mr Trump says he will never drop out of the race to be president and will never let his supporters down.

He has been under pressure after a tape from 2005 of him bragging about groping and kissing women was broadcast.

'Enough!'

The latest to withdraw their support are former Republican presidential candidate John McCain and former Secretary of State Condoleezza Rice.

The Republican National Committee (RNC) sets out in its Rule 9 the terms for "filling vacancies in nominations".

It reads: "The Republican National Committee is hereby authorized and empowered to fill any and all vacancies which may occur by reason of death, declination, or otherwise of the Republican candidate for President of the United States."

Death may be off the agenda, so what about the other scenarios?

Declination...

Many in the GOP are reeling from shock, revulsion and utter confusion about what to do next after a video surfaced Friday of Donald Trump talking about women in crude and aggressive sexual terms.

Mr Trump has been under pressure after a tape from 2005 of him making obscene comments and bragging about groping and kissing women emerged on Friday.

He told the Wall Street Journal there was "zero chance I'll quit" and he was getting "unbelievable" support.

Top Republicans have condemned Mr Trump's remarks in the video.

Since the tape emerged, at least 10 Republican senators have either said they will not be voting for the Republican candidate in the general election in 30 days' time, or have called for him to stand aside.