‘How dare Olly Robbins not have made me look like a chaotic, unprincipled plonker?” is an interesting defence for a prime minister to go for. But we are where we are. Never mind “this is the future liberals want”: this is the past that Keir Starmer wants. What follows is the alternative branch of history the endlessly victimised PM apparently wishes we’d lived through instead.

In this version, he chooses a career liability to be US ambassador, who is well known to have been big pals with a notorious sex trafficker of underage girls and to have spent years involved in questionable business associations, some with Russian and Chinese firms. He immediately announces the appointment. When that guy is deemed a risk by the famously stringent developed national security vetting process – seriously, who’d-a-thunk-it?! – then Starmer has to go out and tell the public that the wrong ’un isn’t actually going to be his US ambassador after all, for “reasons”. Not to be one of the many people who has to explain how basic politics works to the PM, but after that notional fiasco, we’d have spent a very long time indeed talking about his bad judgment. Just like we are now. It’s almost as if all branches of history lead to a discussion about Keir Starmer’s bad judgment. The only person who doesn’t judge this to be the situation is Keir Starmer, which is another instance of his bad judgment. Monday found him chuntering away at the dispatch box like an arsonist complaining about the price of matches.

Alas, this morning saw the prime minister’s victim impact statement rapidly tarnished by Sir Olly Robbins himself, during his appearance before the foreign affairs committee. Robbins reminded the committee that by the time he arrived in his new post as permanent secretary at the Foreign Office, Peter Mandelson’s appointment as US ambassador had already been announced, his name submitted to the king, and he had been through the formal diplomatic process for obtaining approval from the host country – which had been granted, among other seeming faits accomplis. And that none of these announcements had included any suggestion that the gig was subject to vetting. “I believe,” Robbins told the committee, “the Cabinet Office raised whether developed vetting [DV] was actually necessary.” Ooooof. Righto. I mean, what’s the worst that could have happened?

All the above contributed to an “atmosphere of pressure”, Robbins repeatedly emphasised, marked by “constant chasing” by No 10, which applied “constant pressure” to the Foreign Office to fast-track Mandelson’s formal appointment and exhibited – as he again stressed repeatedly – “a generally dismissive attitude to his vetting clearance”. In the end, it was Sir Olly who last week ended up being dismissed. But back to the pressure. In Robbins’s judgment, “the source of pressure was No 10 private office”. More precise details on the provenance of that pressure? “I think the private office would only have been feeling this pressure if they themselves were under pressure.” Who could the active agent(s) of that pressure likely be, other than the organ grinder or his monkey? (Divide those roles between Starmer and his former chief of staff Morgan McSweeney at your own discretion.)

In other news about senior Labour figures since ostracised for continuing their friendships with paedophiles, Robbins revealed that Starmer’s No 10 had initiated several discussions with him about finding a head of mission role – a head of mission role! – for Matthew Doyle, at the time merely the PM’s comms chief, “and I was under strict instruction not to discuss that with the then foreign secretary, which I found uncomfortable”. Go on. “It was difficult for me, personally, honestly, as a leader, to explain why very talented and experienced diplomats were having to leave the organisation and people who would be widely considered to have rather fewer credentials would be input in these important jobs.” In tangentially related news, great that the country is losing a civil servant of the obviously exceptional calibre of Robbins, while certain political inadequates cling on, with even national security processes breached in attempts to shore up their defence.

As for regrets, Sir Olly had a few, but one he did mention was that the due diligence process on Mandelson carried out by the Cabinet Office before Robbins even took up his post at the Foreign Office – and which threw up serious reputational risks – “did not affect the judgment of the prime minister”. In Whitehall, that is quite the telling-off. And of course, back when Starmer was leader of the opposition, his own chief skill was telling people off. He told Tory prime ministers off for years, specialising in a kind of pained, performatively weary delivery that he seems to have regarded as a public service in and of itself.

But now the teller-off has become the permanently told off, and as a reaction to that, Starmer has morphed into the least appealing classroom character of all – the kid who blames everyone else for everything, snitching on anyone he can and dropping them in it to save himself. In recent months he has got rid of a cabinet secretary he appointed, an ambassador he appointed and now the permanent secretary at the Foreign Office, as well as accepting the resignation of the chief of staff he appointed and seemingly delegated everything to. Cleaning up after himself has become a full-time job.

Perhaps it passes the time for someone whose interest in the actual job – being prime minister – remains one of the great mysteries of the political age. Why is Starmer in politics? He comes across as so profoundly uninterested in it all and so staggeringly uninformed about how it works, let alone in how the machine might be bent to his will to achieve specific, coherent goals. Effective politicians with purpose tend to have worked rather more of this out before they sweep to office on a landslide. Technocrats most particularly need to understand the system. Starmer had a very long time to think of it in advance, so what did he mean to do with his victory? What was his programme for government and the arguments via which he would seek to advance it? What were his big ideas? Abstract nouns don’t count. Back on the threshold of power, Starmer proudly announced: “There is no such thing as Starmerism”, while his biographer explained that he was not a politician in the usual sense.

Oh dear. It would have been much better if he had been. Instead, Starmer seemed happy to come across as a bit too good for it all. Unfortunately, he has turned out to be bad at it. The irony that he is now being slowly devoured by the type of impenetrable process he valorises may or may not have escaped him. But sooner or not much later, he will have plenty of time to think about it.

• Marina Hyde is a Guardian columnist