US President Joe Biden has admitted he "screwed up" in the first presidential debate against Donald Trump, but has vowed to fight on until the US election in November.   Donald Trump has told reporters Mr Biden is quitting, while prominent Democrat figures, including Barack Obama, say the current president has their full support.     On today's Daily, Niall Paterson is joined by our US correspondent James Matthews to assess the likelihood of President Biden withdrawing from the presidential race, and what it would mean for the Democratic Party - and the future of America - if he did.        Producer: Emma Rae Woodhouse  Editor: Philly Beaumont  Promotions producer: David Chipakupaku