Sir Keir is just days away from finding out whether his party will trounce or be trounced at the Batley and Spen by-election. The early predictions are more warnings than reassurances, with some senior Labour figures of the opinion that the party has only a five to ten percent chance of holding on to the West Yorkshire seat. In recent weeks the constituency has become a hotbed of distrust, misinformation and a fierce battle between Labour and the Conservatives, with an outside bid from George Galloway and his Workers Party of Britain.
Combined with Sir Keir's poor result at the Hartlepool by-election in May, many have noted that Batley and Spen is probably his last chance to prove that he and his party speak for Britain's working class.
Yet, multiple polls paint a sobering picture.
One recent YouGov question answered by Labour members and the wider public will likely disconcert Sir Keir.
It found that nearly half of those members who voted for the party in 2019 - 47 percent - believe Andy Burnham, the Greater Manchester Mayor, would be a "better" leader than Sir Keir.
Among the general population, 32 percent believe Mr Burnham would do a better job, compared to just 13 percent who think he'd be worse.
This week, a poll commissioned by Sky News found that seven in ten Labour members think Mr Burnham would make a better leader than Sir Keir.
Worryingly for Sir Keir, Mr Burnham has stated that he is willing to step up to the mark should those within Labour want him to.
After he took nearly 70 percent of the mayoral vote while Labour lost another Red Wall seat in Hartlepool, he slammed his own party and the Tories, saying he would follow a "place-first not party-first approach".
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He added: "People are buying into English devolution - they are telling you to deliver more of it not less."
Although his leadership ambitions could be cut short for a number of reasons.
The first, political scientist Richard Wyn Jones said, was that Mr Burnham has no strong support base in Westminster.
He told Express.co.uk: "Burnham's position is both strong and very weak.
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"It's strong in the sense he has a power base and a huge mandate within that power base, but it's weak because he's in the wrong place.
"You can't lead the Labour Party from Manchester and not be in Parliament, not be in the House of Commons.
"And it's not clear to me that he's got a base there."
Another obstacle comes in the form of Labour's entrenched rule book.
Because Mr Burnham has not had a seat in Parliament since 2017, it means he cannot become leader.
Announcing his leadership ambitions - which would mark his third attempt at the job - he said he was more than aware of the rule.
According to The Sunday Times' Gabriel Pogrund, the mayor could target the seat of Blackley and Broughton, held by Labour MP Graham Stringer, 71, as a way of entering Westminster.
Mr Stringer has a majority of 14,000, "and is everything Burnham is not".
He is a "long-term Eurosceptic, a trustee of a think tank that has promoted climate change denial and an opponent of a stricter lockdown in the north west”.
Crucially, Mr Pogrund added: "Burnham's allies, however, believe Stringer could be made to step aside."
According to odds from Betfair, Burnham is a favourite to replace Sir Keir alongside party chair Angela Rayner and Shadow Foreign Secretary Lisa Nandy.
Others in the running are Corbynites Clive Lewis and Rebecca Long-Bailey, recently sacked Shadow Chancellor Anneliese Dodds, and London Mayor Sadiq Khan.