The first Democratic senator has publicly questioned President Joe Biden's election chances, after seven Congress members broke cover and urged the 81-year-old to step aside.

Senator Michael Bennet told CNN he expected the president to lose to Donald Trump by a "landslide", but stopped short of telling him to end his candidacy.

Bennet said the question of whether to carry on in the race was "something for the president to consider". But he said Trump was "on track, I think, to win this election and maybe win it by a landslide".

Questions have been raised about Biden's fitness for office after a stumbling presidential debate performance against Trump late last month.

The president insists he can beat his adversary, and continues to hold support among key allies after congressional Democrats met to debate his leadership on Tuesday.

Mikie Sherrill is the seventh House Democrat who has publicly called on Biden not to run for re-election, saying the stakes were "too high".

She joined other dissenting voices in Congress that include Adam Smith, who told the BBC earlier this week that the party needed to install a "stronger messenger" as its candidate.