Trump claps back at Biden for claiming he had an affair while Melania was pregnant and has the 'morals of an alley cat,' saying: 'I did not have sex with a porn star'

Joe Biden's and Donald Trump's debate hit a jaw-dropping moment on Thursday night when they got into an argument about porn star Stormy Daniels, which led to the president saying his rival has the 'morals of an alley cat.'

Their policy discussion quickly became personal when the two men got into verbal fisticuffs about Trump's legal problems.

It was one of the many personal attacks the rivals hit each other with in the 90 minute debate, even bickering about who was the better golfer. Biden hit Trump hard when he accused him of having an affair with Daniels when Melania Trump was pregnant with Barron. Trump has denied an affair.

The night turned personal about half way through.  

It began when Biden attacked Trump on reports he was seeking a second term in the White House because he wanted retribution against his perceived political enemies.

'The only person in this stage is a convicted felon as the man I'm looking at right now,' Biden said.

Trump hit back by noting Biden's son Hunter was convicted of three felonies related to a 2018 gun purchase.

'We're going to make this country successful again, because right now it's a failing nation. My retribution is going to be success. But when he talks about a convicted felon, his son is a convicted felon. At a very high level. His son is convicted,' Trump said.

And he repeated his claim he is a victim of politics. 

'Joe could be a convicted felon with all of the things that he's done,' Trump said, referring to his policies at the border and in Ukraine. 

Later, he added: 'This man is a criminal. This man — you're lucky. You're lucky. I did nothing wrong. We'd have a system that was rigged and disgusting. I did nothing wrong.' 

Biden hit back hard, bringing up Trump's reported affair and that it happened while Melania Trump was pregnant with Barron. Trump has denied an affair but he was convicted on 34 felony accounts in New York tied to a hush money payments to Daniels made ahead of the 2016 election.

'The crimes you are still charged with and think of all the civil penalties you have - how many billions of dollars in civil penalties for molesting a woman of public, for doing a whole range of things, of having sex with a porn star on the night while your wife is pregnant? What are you talking about,' Biden said.

'You have the morals of an alley cat,' he added.

'I didn't have sex with a porn star number one,' Trump responded. 'Number two, that was a case that was started and moved. They moved a high ranking official at DOJ into the Manhattan DA 's office to start that case. That case is going to be appealed and one we had a very terrible judge.

He also noted 'my poll numbers went up way up you know ... and we took in more money in the last two weeks than we've ever taken in the history of any campaign. I don't think any campaign has ever taken hundreds of millions of dollars came pouring in. Because the public knows it's a scam.'

Trump is expected to appeal his conviction. 

But the personal attacks didn't stop there, going into their ages, congnitive abilities and golf handicaps.

Biden was asked to address voter concerns that, at 81, he is too old for a second term. 

He noted that he used to be the youngest man in politics. He was first elected to the Senate at the minimum age of 30.

'I spent half my career being the youngest person in politics. I was the second youngest person ever elected the United States Senate. And now I'm the oldest this guy's three years younger, a lot less competent,' he said.

Trump, at 78, doesn't face the same questions about his mental capabilities.

Biden wasn't helped by sounding hoarse throughout the night and struggling multiple times to find his words. 

Trump, meanwhile, bragged about his mental prowess, noting he's 'aced' cognitive tests and won two championships at his golf course - 'not even senior' contests but regular.

'I took two cognitive tests, I aced them,' Trump said 'I just won two club championships, not even senior, regular.'

'To do that, you have to be quite smart, and you have to hit the ball a long way.' 

He aded of Biden: 'He can't hit a ball. 50 yards he challenged me to a golf match. He can hit a ball 50 yards. I think I'm in very good shape. I feel that um, is in good shape as I was 2530 years ago. Actually, I'm probably a little bit lighter. But I'm in as good shape as I was years ago. I feel very good. I feel the same.' 

Biden used that to go after Trump's height and weight. 

'You can see he is six foot five and only 220.'

'Just take a look at what he says he is. Take a look at what he is. Look I'd be happy to have a driving contest. For him. I got my handicap, which when I was vice president, down to a six by the way I told you before, I'm happy to play golf. If you carry on bag,' Biden said.

Trump responded: 'That's the biggest lie: six handicap.'

As the moderators tried to shut down the personal hits, Trump said: 'Let's not be children.' 

Biden replied: 'You are a child.'