There were sharp intakes of breath when Angela Rayner got to her feet in the Commons and made it clear she would vote with the Tories against Sir Keir Starmer.
It was the moment the prime minister must have realised he would need to abandon his attempts at damage limitation over the publication of embarrassing vetting documents related to his appointment of Lord Peter Mandelson as US ambassador.
We need to remember it was Ms Rayner who once called Tories “scum”, yet was now finding common cause with them at the moment when this beleaguered prime minister was vulnerable.
With visions of Brutus in the Roman Senate, Sir Keir may well have been muttering “et tu Angela” as he was forced into a humiliating U-turn as his prized reputation for integrity and good judgement was called into question by MPs on government as well as opposition benches.
The old adage in politics is that whoever wields the knife never gets the crown.
It was true for Michael Heseltine in deposing Margaret Thatcher in 1990, it was true with Michael Gove for eliminating Boris Johnson in 2016, it was true (initially) of Rishi Sunak for ending Mr Johnson’s premiership in 2022.
But will it be true for Ms Rayner after her dramatic intervention in Thursday’s debate in parliament over the Mandelson scandal?
The former deputy prime minister is now being openly discussed as a replacement for Sir Keir despite her resignation less than six months ago over her personal tax payments.
As revealed by The Independent at the time, Ms Rayner felt privately she had been betrayed by Sir Keir and his chief of staff Morgan McSweeney over her downfall, triggered by her failure to pay the correct rate of stamp duty on her Brighton flat.
She has since been biding her time on the Labour backbenches, rarely making interventions, and avoiding direct attacks on the government.
While she gave initial support to Andy Burnham’s abortive Commons return last month, she frustrated many of her natural supporters on the left of the party by not engaging with a letter protesting about the Manchester mayor being blocked from standing in the Gorton and Denton by-election. They were also angry that she still had not spoken out about some of the perceived transgressions of the government on welfare and winter fuel payments.
But it turns out she was just waiting for her moment.
Sir Keir is now on the ropes. MPs are openly calling for him to resign and he is about to engage in the latest of multiple resets to save his government, a mere 19 months after winning power with a huge majority.
Labour’s ratings are still on the floor, his personal ratings are even worse, and the upcoming by-election in Gorton and Denton could finish him if he can hold on as long as 26 February.
Ms Rayner knew what she was doing; she has effectively signalled her intention to be a candidate to replace the prime minister.
With Burnham out of the picture, health secretary Wes Streeting seen as too right-wing and too close to Mandelson, Ms Rayner would stand a strong chance of replacing Sir Keir.
The only question now is if she overplayed her hand with her dramatic Commons intervention – or whether she struck at exactly the right moment.
