In the bearpit of British politics, the most perilous threat for Prime Ministers so often comes from behind them.
It is not the Opposition across the despatch box but their own MPs who ultimately are most likely to deliver the fatal blow to their premiership.
So Sir Keir Starmer could be forgiven for jumping at shadows in the dark and labyrinthine corridors at Westminster when MPs return to Parliament for the King’s Speech on Wednesday, if he survives that long.
Friends, just months ago, may now be foes.
Trusted colleagues are withering in numbers by the hour.
Many MPs can be fickle at the best of time, it slightly goes with the job.
However, in a leadership contest some are truly world-class in treachery.
They may swear loyalty to the PM while pledging allegiances to several candidates.
After the May 7 election disaster for Labour, Sir Keir finds himself increasingly isolated and he has just days, possibly hours, to seize the moment and win a stay of political execution.
As his fate hangs in the balance Labour’s July 2024 general election landslide victory must seem a far distant memory.
Prime Ministers are at their most powerful shortly after coming into office.
That power, built on an electoral mandate, the patronage of dishing out ministerial jobs and being the holder of the most senior Great Office of State, slowly drains away until it gets to a point where it becomes punctured irreparably.
For Sir Keir that moment of danger appears to have come surprisingly early, less than two years into his premiership.
The acute threat to his leadership exploded at the weekend from an unexpected quarter.
Catherine West, the MP for Hornsey and Friern Barnet, stunned Westminster on Saturday by threatening to seek to trigger a leadership contest on Monday if the Cabinet did not move against Sir Keir.
The former leader of Islington Council, born in the small Australian town of Mansfield and who speaks five languages including Mandarin, is not seen at Westminster as a natural rebel.
She backed Jeremy Corbyn for the Labour leadership and is a former Foreign Office minister.
Some slighted ex-ministers never give up on seeking revenge.
But Ms West’s threat against Sir Keir does not appear to be motivated by such a desire, instead she believes he must go for the good of the Labour Party and the country.
By early evening on Monday, more than 60 Labour MPs were calling on Sir Keir to quit, many demanding an orderly timetable rather than a chaotic leadership contest.
There were also signs that allies of Health Secretary Wes Streeting may be moving against the PM in what could be a co-ordinated operation.
If so this could trigger a backlash from rival leadership camps.
Ms West’s move echoes that which led to the downfall of Iain Duncan Smith, now knighted, as Tory leader in the autumn of 2003, also after just two years in the post.
At the time, many Tory ministers and MPs were in despair at his leadership.
But it was John Greenway, a slightly gruff backbench MP for Ryedale, North Yorkshire, who had the courage to come out the Tory trenches, go over the political parapet and push for a vote of confidence against Mr Duncan Smith whose fate was swiftly sealed.
It is not yet clear if Ms West’s attempted coup will succeed, as many MPs on the Left of the party want to delay a contest to allow Greater Manchester Mayor Andy Burnham to get back in the Commons so he can stand.
But her move has left the Prime Minister severely wounded.
Now, though, it is also decision time for the MPs who want to seize his crown.
Mr Streeting has made no secret of his ambition to be Prime Minister and a contest now seems to favour him most, despite his past close links to Lord Mandelson.
Former Deputy Prime Minister Angela Rayner still has a tax affairs row with HMRC hanging over her.
She launched a devastating attack on Sir Keir’s premiership but appeared to be playing for time, by backing a Commons comeback for Mr Burnham, while positioning herself in case a contest is triggered as early as this week.
If this happens, Mr Burnham may have to watch from the sidelines after he was blocked by Labour chiefs, including Sir Keir, in his bid to return to Parliament, by torpedoing his attempt to be the party’s candidate at the Gorton and Denton by-election.
But the moment is also fraught with danger for Mr Streeting, and other would-be contenders, as the person who wields the knife rarely inherits the crown.
Once leadership contests start, the outcome is also often unpredictable.
Afterall, Labour elected Mr Corbyn as leader after some MPs backed him just so there was a candidate from the Left in the 2015 contest not expecting for a moment that he would win.
