Boris Johnson becomes Dominic Cummings' human shield

The rule of modern politics, let's call it Trump's first law, is that if you are being attacked for apparently breaking the rules, the best defence is to double down and insist that it is in fact you and your colleagues who have acted with the utmost integrity - and anyone who suggests otherwise is a knave or a fool.

Such was how the prime minister defended his chief aide Dominic Cummings - who as I said just now in the daily Downing Street press conference breached not just one but at least three lockdown rules (don't leave the house if someone in it has Covid-19 symptoms, don't spend hours in very close proximity in a confined space like a car with a sufferer and don't go to a second home).

The PM said of Cummings' 260 mile car journey from London to Durham: "In travelling to find the right kind of childcare, at the moment when both he and his wife were about to be incapacitated by Coronavirus, and when he had no alternative, I think he followed the instincts of every father and every parent.

"And I do not mark him down for that...I believe that in every respect he has acted responsibly and legally and with integrity, and with the overwhelming aim of stopping the spread of the virus and saving lives".

In other words, far from breaking the rules, Cummings is an example to us all, a hero of the national struggle against the cursed virus.

Whether all the PM's MP and ministerial colleagues agree with that encomium is not in doubt: they don't.

But the PM has just become Cummings's human shield. Which is risky for Johnson, but means most of Cummings's critics within the Tory Party will have to pipe down.

It won't stop Labour and opposition parties making hay.

And it may have unfortunate ramifications, not least - in the words of one former police officer - "mass appeals against fixed penalty notices for breaching lockdown rules".

The Cummings defence may well enter the lexicon of reasons why someone is not distancing in the way the government and its scientific advisers would hope and expect.

But the judgement of a number of cabinet members that it's not if but when Cummings is forced out - which I reported earlier today - has to be revisited, even though the norms of conventional politics made their assessment wholly uncontroversial.

What won't be revisited - and was reinforced today by the prime minister - is that everything important about this government is defined as much by Cummings as by Johnson.