Media playback is unsupported on your device Media caption 'He pumps himself up by putting other people down,' says Obama

US Republican presidential candidate Donald Trump and his team have come out fighting after a slew of attacks over his obscene remarks about women.

Mr Trump is due to meet his Democratic rival Hillary Clinton in the second debate at 21:00 local time (01:00 GMT).

His adviser Rudy Giuliani said Mr Trump may well bring up Mrs Clinton's alleged role in discrediting women who accused her husband Bill of sexual abuse.

A 2005 recording of Mr Trump reveals him bragging about groping women.

At least 33 senior Republicans - including senators, members of Congress, and state governors - have withdrawn their support since the video surfaced on Friday.

President Barack Obama joined the criticism on Sunday when he said: "It tells you that he's insecure enough that he pumps himself up by putting other people down."

Mr Trump tweeted a link to a video in which a woman accuses former president Bill Clinton of rape in 1978 while he was attorney general of Arkansas.

Mr Clinton denied her claims of rape when they first emerged in 1999.

Image copyright Reuters Image caption Donald Trump made a brief appearance outside Trump Tower on Saturday to greet his supporters

Image copyright AFP Image caption Hillary Clinton arrives in St Louis

Some Republicans are calling for Mr Trump to quit the presidential race. Utah Senator Mike Lee said the Republican Party had to find another candidate or it would not win the White House.

"We've got candidates who can do it. There's still time to do it, but we have to actually do it," he told NBC's Meet the Press.

Mr Trump, who gave a video apology over the 2005 recording, has said there is "zero chance I'll quit".

And most Republican voters would appear to support his stance. In the first poll since the release of the tape, by Politico/Morning Consult, some 74% of Republican voters believe the party should continue to support him.

A number of his supporters booed a party unity rally in Wisconsin on Saturday night, given by House Speaker Paul Ryan. Mr Ryan disinvited Mr Trump to attend the event after the tape revelations.

Image copyright @realDonaldTrump

Farage says Trump 'alpha male boasting'

In his video apology, Mr Trump gave a hint that he would bring up more lurid allegations in Sunday's debate saying: "Bill Clinton has actually abused women and Hillary Clinton has bullied, attacked, shamed and intimidated his victims. We will discuss this more in the coming days."

Mr Giuliani, former New York mayor, told US media that Mr Trump would not hesitate to describe Mr Clinton's abuse in criminal terms.

"The reality is that... this is a situation in which neither side should throw stones because both sides have sinned," he told NBC's Meet the Press.

Hillary Clinton's camp has not responded to the allegations, but her campaign chairman John Podesta called Mr Trump "disgusting" when asked for his response to the tape revelations. "This is who this guy is," he said.

And it could be risky for Mr Trump to refer to Bill Clinton's infidelities. According to the New York Times, polling suggests a majority of voters are not interested in revisiting stories about Mr Clinton's behaviour.

Media playback is unsupported on your device Media caption While some Trump supporters remain loyal, others are changing their vote

Why is Bill Clinton being targeted?

Allegations of marital infidelity first surfaced when Bill Clinton ran for the White House in 1992. The Clintons went on national television to declare their love for each other, though they did not directly deny the claims of an alleged affair by nightclub singer Gennifer Flowers.

Mr Clinton was a popular president who won a second term in 1996. But his last years in office were beset by scandal and a Senate impeachment trial, after it emerged he had lied under oath about an affair with White House intern Monica Lewinsky.

Rumours of other infidelities, and of Hillary Clinton's aggressive response to the women accusers, have dogged the couple ever since, including the allegations Mr Trump is tweeting about.

Warning: The rest of this article contains some graphic language

The tape recording of Mr Trump dates back to 2005 when he was appearing as a guest on a soap opera.

In it he says, "you can do anything" to women "when you're a star" and is heard saying "grab them by the pussy".

The recording, posted by the Washington Post, overshadowed the release of transcripts of Mrs Clinton's speeches to private events, by the whistle-blowing site Wikileaks.

Further revelations of Mr Trump's language about women emerged on Saturday, when recordings of his conversations with controversial radio talk show host Howard Stern came to light.

In one 2006 conversation, he discusses his daughter Ivanka's body and tells Mr Stern it is okay to call her "a piece of ass".

Media playback is unsupported on your device Media caption Trump apologises for lewd comments and vows to be a "better man"

Media playback is unsupported on your device Media caption Donald Trump makes offensive comments about women

Mr Trump's third wife Melania - whom he married a few months before the 2005 recording and who was pregnant at the time - has called his comments "unacceptable and offensive". However, she said she had accepted his apology.

Former Republican presidential candidate John McCain and former Secretary of State Condoleezza Rice have joined the growing list of Republican politicians who have deserted him.

Some Republicans say they will "write in" Mike Pence, Mr Trump's vice-presidential running mate, on the ballot sheet instead as a symbolic show of opposition to his candidacy.