BBC | Joe Biden's campaign faced further pressure on Thursday amid reported concerns from Barack Obama about the presidential election, a darkening mood among Democrats and polls suggesting Donald Trump was pulling ahead.
Some Democrats painted a bleak picture. One senior party official told the BBC that many in the party felt Mr Biden's stepping down was "inevitable".
Polling on Thursday by the BBC's US partner, CBS News, showed him five points behind Trump - the widest margin recorded this campaign.
But Mr Biden's campaign batted away reports of high-level Democratic concern as "baseless", insisting he would remain the nominee.