Sir Keir Starmer will mark his first 100 days in office this Sunday. When his press spokesperson was asked ahead of the big day if the prime minister thought it had been a successful start, he simply said: “It’s up to the public to decide that.”

The verdict is in, and it isn’t good: Sir Keir’s approval poll ratings last week fell to -33 – a drop of 44 points since his post-election high, while one poll put Labour just one point ahead of the Tories.

A poll out this weekend by YouGov finds nearly half of those who voted Labour in the last general election feel let down so far, while six in 10 disapprove of the government’s record so far, against one in six who approve of the Starmer government.

Sir Keir will no doubt say it’s not about the first 100 days, it’s about the “next decade of national renewal”. And perhaps he has a point. How can you foretell the fortunes of a political leader from 100 days?

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The great late Alistair Cooke in one of his Letter from America dispatches said making a big deal out of the first 100 days was a “foolish custom”.

And in some ways he is right. For a start, how can anyone measure up to the leader this mythic yardstick was used for, Franklin D Roosevelt? He pushed through a record number of laws in his first 100 days in office as he sought to pull America out of the clutches of the Great Depression and confront a national crisis.

Nothing like it has been seen before or since. You can understand why the vainglorious Donald Trump dismissed the 100 days notion as a “ridiculous standard” (while simultaneously caring ever so much and setting up a website dedicated to his first 100 days).

Putting FDR aside, there are reasons why the first 100 days are a useful yardstick. It sets the tone of a premiership and tells us something about a leader’s momentum.

In these early weeks, fresh from an election victory, a prime minister is at the height of their popularity and political capital.

The first 100 days then can be seen as a staging post in which we can take stock and ask whether a leader has met the moment or fallen short.

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100 days Sir Keir might want to forget

For Sir Keir it’s been 100 days he might in many ways want to forget. By pretty much any measure, it’s been a disappointing start. From opinion polls to party management to the operation of No 10, Sir Keir has been in difficulty.

That a prime minister felt compelled to overhaul his top team and replace his chief of staff Sue Gray on the eve of his 100-day anniversary says it all.

Instead of using the first 100 days marker to shout about all the things this Labour government has done, the prime minister has triggered a reset of his government.

The fresh start promised in the election campaign has given way to a false start after his No 10 operation became paralysed by infighting, his personal ratings plummeted after rows over freebies and his government got so lost in itself it forgot to tell the story of change and show that story to the public.

An ‘incredibly frustrating’ start

It has been, admits one senior government figure, an “incredibly frustrating” period in which the work of government has been drowned out by the mess around Downing Street power struggles and rows over concert tickets, spectacles and suits.

“A lot of Starmer’s early decisions have been designed to deliver on the manifesto promises and the economy. We have pushed through renters reform, making work pay, we are setting up GB Energy and pushing through planning reform,” says another senior figure.

“A lot of what we have done is to get things going on that path to deliver for the people. It’s the worst thing for everyone and every member of cabinet not to be talking about the change the country elected us for.

“We have taken a bit of a hit [over freebies] but I think it’s fixable because it’s optics rather than wasting taxpayer’s money. It’s more about a country that wants to see the PM lead on issues they care about – the cost of living, the NHS, the economy – and when they don’t see that, it’s frustrating.”

‘What poor conditions the country is in’

It has also been, admit No 10 and No 11 insiders, much more difficult than they anticipated.

Be it the race riots that ripped through our cities shortly after Labour was elected, to the crisis of prison places or the problems of immediate funding shortfalls the chancellor says she’s identified, the new administration has been beset by challenges.

“It’s been very clear this first 100 days what poor conditions the country’s in,” says one senior government figure.

Overlay that with the crisis in the Middle East and the ongoing Ukraine war, and this is a prime minister and new team with a very full plate indeed.

But what has also been clear these first 100 days is what poor condition the prime minister’s operation is in.

The prime minister has taken a huge gamble

You may not know the characters behind the big black door of No 10, or what they do, but what will be obvious to you is that having to overhaul the operation within the first three months of government because it has become dysfunctional, toxic and not fit for purpose, doesn’t bode well.

Because it raises a very acute question: if a prime minister can’t run Downing Street, how the hell is he going to run the country?

That Sir Keir moved to clean up his No 10 operation last week was a defining moment for his first term in office.

By moving out Sue Gray as his chief of staff – the most powerful unelected figure in government – and replacing her with his trusted ally and key political aide Morgan McSweeney, the prime minister has taken a huge gamble.

That’s because he’s swapped out an experienced Whitehall operator with over 30 years of experience in government with a political strategist who is the brains behind the election victory. But the big unknown is whether Mr McSweeney can run the government like he ran the election.

Has McSweeney got the experience to run the government?

The whole point of bringing Ms Gray into the No 10 operation is because she understood the machinery of government and how to pull the levers of Whitehall to get things done.

Mr McSweeney might be a brilliant political operator but has he got the experience to actually run government? Sir Keir presumably in the past concluded he had not, which is why he hired Ms Gray.

Friends of Ms Gray tell me she thought Sir Keir needed to pad out the team who ran his office as leader of the opposition with more big beasts now he was running the government.

They say she pushed to bring in new people who she thought had the necessary experience – the reason Sir Keir didn’t have a principal private secretary, a crucial mandarin for any prime minister, until Ms Gray was removed was because she and others were locked in a turf war over it.

You know the tensions that ensued as Ms Gray went to war with advisors – over their job titles, their access to the prime minister, their salaries, their readiness for government – because she became the subject of endless briefings.

The more Ms Gray was in the press, the more untenable she knew her position would become with a prime minister running out of patience.

Sir Keir did move and moved decisively. But that his operation got so toxic, and that some on his team kept up the briefing wars despite him absolutely hating it, doesn’t bode well for the prime minister: it speaks to dysfunction in his operation – and it is rarely one individual from which that dysfunction flows.

Starmer would probably like to start again

The prime minister can at least take comfort from the fact much of the criticism a leader faces in the first 100 days doesn’t have to define the success of a leader.

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President Bill Clinton got off to a shaky start in his first term and went on to become the second Democrat president since Roosevelt to win a second term.

But if, as one of Sir Keir’s allies tells me, “every day in government matters”, then you also have to conclude Sir Keir’s first 100 days have been a horrible waste as the prime minister scrambled to set the agenda and keep his own house in order.

He is a prime minister who would probably like to forget his first 100 days entirely and start again.

There will be an investment summit on Monday and the budget later this month. The goal of this government is to “be boring” and get back to the business of governing.

The next election is a long way off, Sir Keir has a big majority and a massive megaphone.

He can perhaps afford to write off these first three months if he gets the next few right. But after one false start, he can’t afford another.