Donald Trump’s presidential campaign is under threat after a video of the billionaire bragging about groping, kissing and trying to have sex with women was revealed, prompting senior Republicans to withdraw their support.

On Saturday (AEST) The Washington Post published footage from 2005, showing Trump speaking to then-Access Hollywood host Billy Bush about sexually assaulting women and getting away with it because he was famous.

And in a campaign that’s been riddled with Trump misdemeanours this is the scandal that could cause his bid for the presidency to collapse.

Here’s why.

1. Significant Republicans lambast Trump

According to the New York Times, 42 prominent Republicans have withdrawn support for Trump since the video leaked.

Even Trump’s closest ally, Mike Pence, rebuked the billionaire. Photo: Getty

In fact, 150 Republican figures have dis-endorsed Trump since mid-June 2015, but the 42 who have done so following the video scandal have been high profile.

That’s added to the important Republicans who launched stunning rebukes after the video surfaced.

Leading the denouncements were Republican National Committee chairman Reince Priebus, 2008 Republican nominee John McCain (also withdrew support), Congress Speaker Paul Ryan, Senate Majority Leader Mitch McConnell, Trump’s own vice-presidential nominee Mike Pence, senior figure Jason Chaffetz (also withdrew support) and 2012 Republican nominee Mitt Romney.

Former governor of California Arnold Schwarzenegger, former Secretary of State Condoleezza Rice, Governor of Ohio John Kasich and candidate for the 2016 Republican nomination Carly Fiorina also all withdrew support for Trump.

2. Voting has already begun

Americans are already going to the polls despite the November 8 election day.

More than 400,000 voters in 18 states have cast ballots, ElectionProject.org estimated. Many more are expected to vote before election day.

The only way Trump can be replaced as the Republican candidate would be for him to die or step down. Trump tweeted that wouldn’t happen:

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! #MAGA

— Donald J. Trump (@realDonaldTrump) October 8, 2016

3. Trump described sexual assault

Racism, misogyny, elitism, veiled threats of violence, alleged tax evasion and mocking the disabled are some of the heinous accusations Trump has overcome thus far.

Commentators and rivals had extrapolated from Trump’s behaviour that he is a man who with questionable ethics and has an unhealthy attitude towards women.

Trump walks arm in arm with the woman he disparaged, and interviewer Bush. Photo: YouTube

But none of those accusations illustrated as vivid a picture of a cavalier attitude toward sexual assault as this video had.

Jessica Valenti wrote in The Guardian: “If we want to believe – as we should – that sexism is aberrant behavior in men, then we can’t excuse what’s on this tape as commonplace.

“Sexually assaulting women is not normal, if even if it is routine. And as familiar as that stomach-churning interaction is to women, it’s also one we won’t accept as our lot in life.

“That’s why Trump won’t recover from this tape.”

4. A common, real response

Many journalists, commentators, the politically engaged and politicians themselves have long been damning of Trump.

So too have everyday people, but not in the way they had been after Trump’s alleged description of sexual assault. The early signs are that this scandal may have the sort of cut-through that changes voters mind.

Canadian writer Kelly Oxford asked women to tweet about their first sexual assaults after the Trump video went viral.

https://twitter.com/kellyoxford/status/784541062119456769

Ms Oxford was inundated with responses. More than 9.7 million people engaged with her tweet, while according to her she received 50 replies per minute for 14 hours.

https://twitter.com/kellyoxford/status/784934911887106048

https://twitter.com/kellyoxford/status/784758511347511296