After two weeks of calls for him to step away from the presidential race, Joe Biden has finally set out his criteria for ending his five-decade political career.

In his press conference at the Nato summit on Thursday, he said that he would stay in the contest unless his team told him: “There’s no way you can win.”

“They’re not saying that,” he insisted. “No poll says that.”

That stance is a change from his previous pronouncement that only the “Lord Almighty” could persuade him to make way for a younger candidate.

It came after accusations from sitting Democrats that Mr Biden’s belief he is the only man who could beat Donald Trump risked losing his party the presidency and both branches of Congress in November’s election.

On Thursday, he acknowledged: “There are other people who could beat Trump, too. But it’s awful hard to start from scratch.”

The polls already suggest that he will lose the election, and his advisers are already working out how to break that news to him.

David Axelrod, the former Barack Obama campaign adviser, has speculated that Mr Biden’s inner circle may be hiding the truth from him about his poor performance in the polls.

Mr Biden had something of a comeback earlier this year, after entering 2024 behind Trump in national polls.

He increased his support from 44.4 per cent to 46.7 per cent of the US public, halving the gap between him and Trump from 2.2pts to 0.8pts by the end of May. 

Analysts suggested that the improving economy was finally being noticed by voters.

The polls tightened further when Trump was convicted in the Stormy Daniels “hush money” case. 

Within a week of the jury’s verdict, the gap between him and Mr Biden had shrunk to just 0.3pts.

But the constant focus on the 81-year-old president’s age and health has since seen the polls fall back. 

Since May, the gap between the two men has jumped to three points, as Mr Biden’s own support has plummeted down to 44.2 per cent.

This has generated significant scepticism that he could beat Trump in November, after months more scrutiny of his age and gaffes.

The US betting markets now give vice president Kamala Harris a better chance of winning the 2024 race than Mr Biden, although both are significantly behind Trump.

On Thursday, Mr Biden claimed: “There are at least five presidents running or incumbent presidents who had lower numbers than I have now.”

Although strictly true, he neglected to mention that none of the incumbents with lower numbers won their elections.

George HW Bush, Jimmy Carter and Trump had similar approval ratings at this point in the presidential cycle, but all lost their races for re-election and left the White House after just one term.

At this point in the 2012 cycle, Mr Obama was leading Mitt Romney by 2.5 points. Trump was trailing Mr Biden by eight points.

Part of the issue for Mr Biden’s campaign is that his support is falling among groups that were most likely to vote for him in 2020, including young liberals and minority ethnic Americans.

That trend is driven partly by his stance on the war in Gaza, which has alienated pro-Palestinian Americans. 

Those voters are unlikely to support Trump, but may pick a third-party candidate or choose not to vote, experts believe.

Meanwhile, Mr Biden has also been losing some of the voters in camps where Trump was already leading.

Since November 2023, his support among middle-aged people has fallen from 44 per cent to 37 per cent, the proportion of men who back him has fallen from 37 per cent to 34 per cent.

He is also neck-and-neck with Trump among Hispanic voters, where the Trump campaign has made some of its largest gains.

The nature of state-by-state voting in presidential elections means that Mr Biden’s national ratings are less important than his support in several key battleground states.

If he loses the majority of the swing states, Trump will win the election, even if he has strong support in some true blue areas, like California.

Trump was already leading in the key states, but since the end of May when he was convicted, the polls suggest the gap has widened further.

That is true in Arizona, Wisconsin, Michigan, Pennsylvania and North Carolina.

In four of these states, the gap now exceeds five points – at the start of 2024 it was just two states.

If Trump picked up just those states with leads of five points, he would win the presidential election by 271 electoral college delegates to 266, the polls suggest.

Mr Biden’s aides have argued that the slump in support he has experienced since his disastrous debate with Trump two weeks ago is temporary.

They say that he has experienced a campaign “moment”, rather than a fundamental shift in the race.

But as his performance at Nato showed, there is serious potential for more slip-ups that will erode his support further. The additional scrutiny on everything the president does is unlikely to work in his favour.