The ultimate debate referee - a fact-checker - is looking into up to 20 claims from the latest Hillary Clinton-Donald Trump presidential bout.

LISTEN ABOVE: Senior correspondent for Politifact, Louis Jacobson spoke to Andrew Dickens

Senior correspondent for Politifact, Louis Jacobson, said they're looking into more of Trump's claims than Clinton's.

He told Andrew Dickens Trump can actually be quite hard to fact-check because he is often incoherent, saying one thing, and then saying the complete opposite.

Among other things, the Republican candidate threatened Hillary Clinton with jail as he tried to keep his troubled campaign alive in a fiery re-match.

There was a brutal exchange of words between the pair from the get-go.

And CNN's Mark Preston says Trump needs to show he can step back, rather than go for the jugular.

"The idea that Donald Trump, when he gets punched once he wants to punch you four or five times. As leader in chief and as the leader of the free world sometimes you need to take a step back and take a deep breath.

"The bottom line is that women right here in the United States more alienated from Donald Trump. Quite frankly you're going to see that from men as well and it really comes down to the issue of temperament."

Early figures show the second debate's unlikely to have had as many viewers as the first.