Boris Johnson is fighting to keep his job.

The UK prime minister and his operation in Downing Street are under police investigation, and in the last 24 hours two more backbench MPs from his own Conservative Party, Peter Aldous and Tobias Ellwood, have called on him to resign. 

The two have also announced they'll be sending in letters of no confidence to party officials. If 54 of those letters – 15 percent of the party's 359 MPs – are sent, it will trigger a vote on his leadership. At the moment there's no suggestion of a flood but the trickle remains steady.

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But after the release of the latest report into Downing Street parties, Johnson was on a plane for front line meetings with the Ukrainian President. And at Prime Minister’s Questions the Prime Minister seemed buoyed rather than cowed by these challenges.

His opponent Keir Starmer attacked his performance on taxes and the economy, choosing to avoid so-called 'partygate' apart from a couple of crafty jokes about police questions. It was left to the Scottish National Party's leader in Westminster, Ian Blackford, to pick up the baton and demand answers about a particular party on November 13, 2020. 

That event is now part of the police investigation, but it's known to have taken place, not in the Downing Street offices, but in the residential accommodation upstairs. That distinction will be of great significance to the police, as will clarification of whether or not Johnson was there at the time.

He declined to answer on this occasion and Blackford replied that the prime minister had become "a dangerous distraction at home, and a running joke on the international stage."

It's not clear yet whether the police investigation helps or hinders the prime minister's cause. A confirmed, and even prosecuted, case of breaching lockdown rules would be a huge blow to his reputation. But the deliberations and delay that will surely result from detectives doing their work may yet lead to a drift in his enemies' agenda.

Should a combination of Ukraine, the economy and control of COVID-19 place Johnson back in a favorable light, the public mood could change. In terms of what they're prepared to forgive or simply forget, the British public are a very difficult constituency to predict.