“Look what happens when the Labour Party moves so, so far to the left,” Joe Biden said following Jeremy Corbyn’s election defeat in 2019. 

Democrats in the centre of the party seized on Labour’s loss to Boris Johnson as proof Bernie Sanders could not beat Donald Trump.

One year on, Biden is on the verge of capturing the White House having staged a dramatic comeback against the Democratic left in the primaries. 

Now the lessons are flowing the other way across the Atlantic, says YouGov’s Marcus Roberts. The pollster’s director of international projects says the former vice president is offering Keir Starmer a “template” of how to win.

“Lesson number one is the candidate is the centre of gravity,” he says. “You need to be ahead on favourability, ahead on approval numbers, whether that’s best PM or best president. If your candidate leads on those things, that can buy you the space for lesson number two, which is policy can be radical if the candidate is reassuring.

“Biden is running on the most progressive and liberal platform that the Democrats have had since FDR, or potentially ever,” he says. “However everything about him screams normalcy. 

“He is there as the guarantor that nothing crazy is going to happen in America after the Democrats are elected — even as he is proposing some of the most far reaching economic and social reforms the country has ever seen.”

Roberts, who has worked for both Labour and the Democrats, sees a “lot of parallels” in personal style between Biden and Starmer. “They are not fire-breathers, they don’t naturally energise and inspire their party’s bases, but they do speak to the common sense values of the mainstream of their nations.”

The third lesson Roberts says the Democrats can teach Labour, is that if they win it will be because the Biden campaign correctly identified the “blue-collar Trump/Obama voters as the most important voters in the election”.

“If Starmer wins it’s because similarly he’ll have won not just the ex-Labour red wall/blue wall voters back, but voters who are like them across the whole of the UK, in Wales and in Scotland as well,” Roberts says.

There was, what Starmer aide Jenny Chapman described as “encouraging”, news for Labour today with the Ipsos MORI poll for the Evening Standard that showed the party had jumped to a five point lead over the Tories. Stamer holds a net personal satisfaction rating of +15@ while Johnson has slumped to 26%, his worst ever rating he’s had with the pollster since he became PM.

But the poll was conducted before Labour was found to have unlawfully discriminated against and harassed Jewish people. And before Jeremy Corbyn was suspended from the party for his response to the Equality and Human Rights Commission report.

On his media round this morning Starmer said while there was “no reason for a civil war” it didn’t sound like he wasn’t willing to fight one. And he left open the possibility, while stressing it was not his decision, that Corbyn could be expelled. Starmer may have had one eye on last night’s YouGov survey showing the public backed the decision to suspend his predecessor by 58% to 13%.

There were signs today however of figures on the left publicly moving to try and stop the anger from Corbyn’s supporters spilling over into all out war.  

John McDonnell said his advice as an “elder statesman” was to avoid the party “drifting towards a hell of a row over use of language, misinterpretation, followed by overreaction”. Jon Lansman added there needed to be more “diplomacy” from the left, “fewer war cries”, and “a lot more concern for the victims of racism”. And Len McCluskey, Unite’s general secretary, said while Corbyn’s suspension was “wrong” and “unjust”, “now is the time for some calmness”.

But Momentum, the grassroots campaign group, is tonight holding a rally in defence of Corbyn and said his suspension made a ’mockery” of Starmer’s pledge to unite a party that was now “more divided than ever”. Diane Abbott, Richard Burgon and McDonnell are due to speak.

In the US, a civil war running into the general election was avoided and Sanders largely swung in behind Biden after a fractious left-right primary battle. And in October he resumed in-person campaigning for the former vice president in a show of party unity.

Whether that final lesson will be one Labour wants to learn remains to be seen.

Also of course, Biden might lose.