Yes, it really is only 496 days since Sir Keir Starmer won a colossal general election landslide.

That feels like a different era this morning: a morning on which health secretary Wes Streeting, the government's designated interviewee on the early media round, has variously accused those at the top of government of a "toxic culture", of sexism, and called for unnamed officials in Downing Street to be sacked.

He was responding to briefings from allies of Sir Keir that the prime minister would fight any challenge to his leadership, with Streeting's name mentioned as a potential challenger.

Let's rewind.

Why is this all playing out today?

There's a longer-term cause and an immediate cause.

The longer-term cause is that this government is very unpopular. That is the reality displayed by poll after poll. According to some, Sir Keir is the most unpopular prime minister in British history.

Labour MPs look at those very same polls and supplement them with their own grim experience of campaigning in their constituencies week-in-week-out.

And then they worry for their own jobs, even if the next general election is a long way away.

That dynamic means that for some months now it has been typical in conversations with Labour figures in Westminster for them to muse upon whether a change of leader would improve their political predicament.

The general assumption among Labour MPs had been that the critical juncture would be in May after elections in Scotland, Wales and parts of England.

But increasingly in recent weeks, with the polling picture remorselessly bleak and anxiety in Labour ranks about what may well prove a controversial Budget, there have been mutterings that Starmer might be challenged sooner rather than later.

One Labour MP told me earlier this month: "It's all very well to say wait for the locals, but that's my activist base I'm sending into the gunfire. I can't lose all my councillors."

It's this sense that things may come to a head faster than appreciated which appears to have sparked an extraordinary briefing operation from allies of the prime minister to us at the BBC, as well as various other outlets.

Letting it be known that the prime minister would fight any challenge to his leadership rather than going quietly may well have been designed to shore up Sir Keir's position, by reminding Labour MPs of the costs - political and economic - of opening up that can of worms.

That was high-risk enough - it's not generally the done thing in politics to advertise your own weakness - but the decision to identify Streeting as someone coveting the top job was especially incendiary.

It's worth noting that some around Sir Keir are also concerned about the ambitions of Shabana Mahmood, the home secretary, Ed Miliband, the energy secretary and former leader, and Lucy Powell, Labour's new deputy leader - who was essentially elected in defiance of Sir Keir.

Streeting, who admitted on the Today programme that he had not heard from the prime minister since last night's briefings, has spent the morning pledging loyalty to Sir Keir while denouncing his broader Downing Street operation.

That's a delicate balance to strike, especially when so many Labour MPs are eager to understand the extent to which Sir Keir himself will have been aware of or implicitly encouraged last night's briefings.

The key question this morning is whether the briefings have made Sir Keir more or less vulnerable.

Judging by the rancour of the messages I have received from various corners of the Labour Party, the definitive answer is: more vulnerable.

One senior Labour figure questioned why Sir Keir's allies had "legitimised what was a taboo" by publicly entertaining the prospect of a leadership challenge.

One minister said "this is pathetic," while another called the briefings "crazy".

An MP said the approach was "utterly unhinged and self-destructive," adding: "They're in the bunker shooting everyone who's outside the bunker guarding it. And poor oblivious Keir doesn't even realise he's in the bunker."

However, a cabinet minister expressed hope that the bitterness of this morning would eventually mean things calm down.

"These are the moments where you look over the cliff and don't like what you see at the bottom."

Sir Keir will no doubt be put under intense pressure by Conservative leader Kemi Badenoch at prime minister's questions at noon.

He will need to draw upon all his reserves of deflective parliamentary wit. Perhaps the most interesting thing though will be the body language of the hundreds of Labour MPs sitting behind him.

One cabinet minister dreading today's PMQs said to me this morning: "I spent all that time in opposition at PMQs pointing at them and laughing and thinking, when we're in power and get our act together it won't be like this.

"So it's going to be galling. And the public just look at us and the Tories and think it's all the same."

And remember - it's only 14 days until the Budget in which Chancellor Rachel Reeves will make huge and potentially manifesto-busting judgment calls.

She now does so against this fevered backdrop. (BBC)

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