Michael Bennet: First Democratic senator questions Biden candidacy

Elsewhere in Washington, congressional Democrats emerged from their private talks. Some chose to speak to reporters, touting Mr Biden’s record in the White House or speaking of Democratic unity.

But the same day, a seventh House Democrat – Mikie Sherrill of New Jersey – publicly called on Mr 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.

In his comments to CNN, Mr 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”.

The Colorado Democrat framed the issue as “a moral question about the future of our country”.

Two other senators are reported by CNN to believe that Mr Biden cannot win the White House again, although neither has publicly broken ranks.

Mr Biden reportedly also faces doubts from diplomats visiting Washington for the Nato meeting, one of whom anonymously told Reuters they could not see him staying in post for another four years.

As the debate lingers – and the White House faces questions about its approach to disclosing information about Mr Biden’s health – speculation continues to grow over who would replace Mr Biden if he chose to step down.

Vice-President Kamala Harris is earning some high-profile backers, despite her ongoing vocal support for the president. During a rally in Las Vegas on Tuesday, Ms Harris insisted her boss was a “fighter”.

Mr Biden himself has dared his doubters to either challenge him or unite behind his candidacy, although he has admitted he “screwed up” in the Trump debate.

His performance in the head-to-head has been ridiculed by his rival, who has suggested Ms Harris would be a “better” competitor for the White House.

But in his latest comments on the matter, Trump said he expected his adversary to stay in the race: “He’s got an ego, and he doesn’t want to quit.”