How difficult would it be for Democrats to replace Joe Biden on presidential ticket?

There is no evidence the US president is willing to end his campaign for re-election (Ross D Franklin/AP)

US President Joe Biden’s halting debate performance has led some in his own party to question whether he should be replaced on the ballot before November.

There is no evidence Mr Biden is willing to end his campaign, and it would be nearly impossible for the Democrats to replace him unless he chooses to step aside.