With Donald Trump's UK state visit days away, Mandelson blame game begins

And now, as questions are being asked about Mandelson’s proximity to meetings with Epstein and what he subsequently did or did not tell No 10, the political cost for Sir Keir is stacking up.

At Prime Minister’s Questions this week, the Labour leader found his normally razor-sharp attacks on the prime minister fumbled, and his backbenchers, and the country, will wait and see if anything more damaging emerges.

Sources tell me the impact on internal polling at No 10 has not been great so far. It’s said to have been minimal, not least because the prime minister was deemed to have acted squarely on the information about Mandelson once he learned it.

But the continued questioning about how Mandelson got the job in the first place has left a major political mark that is not going away.

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“He sure has a lot of introspection and mulling over to do about the structure and processes in place within Number 10 Downing’s staff pool,” said one insider.

Mandelson, now in DC, has told reporters he has never led anyone to believe anything other than what he had said all along; he had been “honest, genuine, and truthful”.

That ultimately will be the crux of the Downing Street investigation – did he do enough and say what he ought to have said to keep No 10 informed?