US presidential candidates Donald Trump and Hillary Clinton squared off in an intense second debate as the Republican candidate came out swinging following the release of a recording of his lewd talk about groping women. Sunday's debate started off with a discussion about whether Trump is fit to be commander-in-chief given the way he has spoken about women. He repeated what he said after a tape of his sexually charged comments in 2005 surfaced, that it was "locker-room talk" that he was not proud of. The event at a campus in St Louis, Missouri, followed a town-hall format where the audience - all undecided voters chosen by the the Gallup Organisation - asked half of the questions on "topics of public interest". Other comments came in from social media users.