Boris Johnson’s great strength has always been his ability to spot, recruit and hire a great variety of brilliant people. He did so when he edited this magazine and as London Mayor with a superb crop of deputy mayors. As Foreign Secretary he couldn’t hire anyone, so he struggled. As Prime Minister, his gift seemed to have come back when he hired Munira Mirza as policy chief. She was one of his deputy mayors and having her in No. 10 was, to me, a promise of great things to come. Her resignation, today, suggests a prime ministerial team that’s falling apart rather than being rebuilt.

She is an academic, a thinker, a fighter, writer (she once wrote a superb cover story for us) and I always saw her as a potential London mayoral candidate. Her Race Commission was one of the best things to come out of Johnson’s Downing Street — and had her hallmarks. Thoughtful, thorough, brave (it meant her taking on the race relations establishment who tried to discredit destroy her) and fundamentally progressive. Her vision of Britain is a genuinely post-racist society: she is vehemently opposed to an identity politics that sees skin colour first and character second. To young Tories, this agenda – which some refer to as culture wars – is the new Conservatism and needed to be fought with vigour. Free speech needs be defended, and she saw this as very much the government’s business.

But others disagreed: Carrie Johnson thought this needlessly divisive and when Dan Rosenfield arrived as Chief of Staff he wanted to dial it all down. His arrival appeared to coincide with a diminution of Mirza’s influence in No. 10: perhaps he thought she picked too many fights. As I wrote in the Daily Telegraph, this left No. 10 at sixes and sevens with identity politics,  not knowing whether to fight it or join it; whether to see these various campaign groups as stakeholders to be assuaged or opponents to be crushed. Johnson was, in the end, undecided.

If Johnson is to recover, he needs to rebuild a team and ought to have based that around Mirza, giving her more authority and leeway. But instead people are leaving him. In her case, she says it’s because he made that Jimmy Savile joke and told her he’d apologise but didn’t. I suspect she looked at his disintegrating No. 10 and concluded that the show is over. Mirza has worked with Johnson for 14 years and will be a good judge of this. He once named her amongst the five women he most admired. That admiration no longer appears to be mutual.

There was some inevitable bloodletting last night – perhaps departures that were going to happen anyway, but pushed through when Mirza left. Rosenfield, who has been speaking about the need to fall on his sword for some time, is off. Jack Doyle, the No. 10 press chief, has also quit saying he always planned to leave after two years. Martin Reynolds, he of the ‘bring your own booze’ email, is returning to the Foreign Office (if he ever makes ambassador, his parties should be legendary). Out, out, out. And no one new in.

Johnson really needed to give a story of renewal: ie, to actually hire great people. He seems unable to do so. To lose Mirza was unexpected (her husband still works there) and pretty depressing for those who hoped this week would mark a BoJo recovery. If he was going to get through this, she’s precisely the sort of person he’d need at the centre of his recovery agenda.

No. 10 is now losing key staff as much as Trump’s White House did.  I’m struggling to think of a prime minister who was able to recharge, renew and refresh once the exodus got underway. Johnson has spent his life defying expectations of political death. He may yet survive. But it’s becoming increasingly hard to see how.