No 10's misjudgement over Mandelson has left Labour MPs increasingly aware of the fallibility of the PM and his team.
The debacle of last summer, when Keir Starmer caved in over welfare reforms after promised concessions failed to convince his mutinous backbenchers, was viewed as a low point for his government. Now, amazingly, it has happened all over again.
If the repetition of history was not already enough, with the ructions over releasing government documents about Peter Mandelson, once again Starmer has a certain Angela Rayner to thank, in part, for digging him out of a political hole.
With welfare reform it was the then-deputy prime minister who bluntly told Downing Street that their offering to Labour MPs was not enough to prevent a likely Commons defeat, prompting No 10 to drop the bulk of the plans.
On Wednesday, Rayner was a key voice advocating that the intelligence and security committee (ISC) should vet the Mandelson files, not No 10, a decision eventually adopted by the government in its amendment to a Conservative motion.
To add to the parallels, another leading figure to push for the ISC compromise was Meg Hillier, senior Labour backbencher and one of the leaders of the welfare rebellion.
There are differences. The welfare plans were months in the making, and a key plank of the government's programme. The chaos over what Starmer did or did not know about Mandelson before making him ambassador to Washington was, instead, a result of US authorities releasing new files about Jeffrey Epstein and his associates.
But the consequences are the same: a weakened Downing Street, and Labour MPs increasingly aware of both their own power and the sheer fallibility of Starmer and the team around him. And as with welfare, this is a crisis delayed, not removed.
While MPs' emotions can often be as infectious and overwrought as a boarding school in exam season, the reaction among many Labour backbenchers to No 10's misjudgement over Mandelson was genuinely furious, a mood not helped by the obvious glee and success with which the Conservatives seized on the issue.
It was the Tories' decision to use one of their intermittent opposition day debates to seek the release of documents setting out Mandelson's appointment which triggered Wednesday's drama.
For well-functioning governments, opposition day debates are an irrelevance. For those with their backs to the wall they can be treacherous - it was a chaotic response to a fairly standard Labour motion on fracking which toppled Liz Truss.
And after the concessions, backbenchers will want action: a swift and comprehensive release of the Mandelson chronology, one that some MPs will hope is sufficiently damning to spell the end Starmer's chief of staff, Morgan McSweeney, Mandelson's main advocate inside No 10.
This is, however, a complicated process, in part because of a now-ongoing police investigation into whether Mandelson passed on insider information to Epstein, an inquiry Starmer warned cannot be prejudiced.
Similarly, if MPs are hoping for a full rundown of how Mandelson was vetted for the job, they will be disappointed, given that the release of even slightly personal information about him would breach data protection rules.
Downing Street will hope that, in a common tactic for beleaguered governments, boring procedure will take the urgency out of the debate, as the ISC pores over a mass of documentation, deciding what can or cannot be released.
This is, however, just a temporary solution to a symptom of what pretty much all Labour backbenchers now view as a wider malaise: the sheer inability of Starmer and his team to regularly make the right call.
A prime minister with better political judgment, they argue, would have ignored the calls to send a man with a long history of controversies and known Epstein links to the Donald Trump court, and either stuck with the highly successful incumbent, career diplomat Karen Pierce, or seek a like-for-like replacement.
Starmer did not, and thus spent prime minister's questions hounded by Kemi Badenoch until he finally accepted that yes, he did know the extent and longevity of Mandelson's ties to Epstein when he offered him one of the most prestigious jobs in the public arena.
And now we have another U-turn, Badenoch claiming a victory, and a cheery-looking Rayner holding court in a Commons corridor. The bulk of Starmer's MPs, meanwhile, are left wondering how many more chances he can get.