AN invisible menace, stealthily growing stronger as its host grows weaker. It spreads unseen, infecting all around it, until it is too late to undo the damage. Its victims are left hollowed-out shells. There is no known cure.

Well, Dominic Cummings is invisible no more. The Prime Minister’s chief adviser, crutch and Achilles’ heel this week became a household name. And other names.

The immediate row over his breaking the lockdown appears to be fizzling out. By Thursday, it had come down to whether he “might” have breached regulations yet dodged a £60 fine. You know a story is on its last legs when it reaches that level. People don’t quit over never-levied £60 fines.

But when you remember the big picture, the outrage comes roaring back. It is clear Mr Cummings should no longer be in his post.

Not for breaching a regulation - though he did - but because he violated the very essence of the lockdown: self-denial for the greater good.

Despite helping to craft and promote the Stay Home, Save Lives message, he broke faith with it and put self-interest above collective interest.

While others selflessly resisted their instincts, he claimed following his had been a virtue. It was pure hypocrisy.

He tells us he left London for Durham because he feared he and his wife were getting sick with Covid and needed help looking after their four-year-old. In other words, he and his family might have faced hardship. Join the club, Dom. It’s hardship all round.

Sick parents cooped up with needy children are, sadly, all too common.

It is not an exceptional experience or exceptional excuse. Mr Cummings may regard himself as exceptional, but that is a different matter.

As for his yarn about a 60-mile round trip to Barnard Castle to test his eyesight, where to begin?

It was as believable as a giant coronavirus particle sitting in the Downing Street garden complaining it wasn’t harmful just misunderstood.

This was no eye test, it was a jaunt to a beauty spot on his wife’s birthday.

Mr Cummings could have edged solo round a few backroads or a deserted carpark to check if he could drive back to London, but somehow he and his family ended up stretching their legs by a picturesque riverbank.

Durham Constabulary didn’t find it credible, and nor did anyone else.

This week has seen the worst side of politics - tribe before country.

Tory ministers have twisted, dissembled, debased themselves, and patronised and insulted the public to protect Mr Cummings and a PM who relies on him to an unhealthy degree.

They have refused to acknowledge failings, brushed aside manifest dishonesty, and even pretended A-roads are good spots for eye tests. They have treated voters like sheep.

To cap it all, they had the gall to tell people to “do the right thing” as we move into the test and trace phase.

To their credit, many Tory MPs and MSPs refused to join the sycophancy.

But aside from Moray MP Douglas Ross, who quit as a Scotland Office minister, it looked like a government of creeps, without honour, without shame.

The collapse in moral authority damages the health messages.

When Matt Hancock chirpily urged people to do their civic duty, as if nothing had happened, my immediate reaction was a disgusted “screw you”.

I’ve since calmed down, but some will take the Cummings approach.

Instead of the right thing, they will do the convenient one. Instead of living within the guidance, they will see how far they can stretch it, the war on the virus undermined by a shift towards spivvy rule-bending.

Mr Johnson may be relieved this weekend to have kept his man in post, but the price for his premiership is enormous. He has antagonised both his party and the electorate.

A few weeks ago, the country fretted when the PM lay at death’s door. Now he’s an object of derision, viewed as a weak leader in thrall to a smarter underling. Some turnaround.

Setting Covid aside for a moment, this should in theory be the honeymoon for Mr Johnson’s government. Less than six months since the election, it should still be enjoying broad support.

Yet this week YouGov found 42 per cent of voters already disapprove of its record, against 37% who approve, and the Tory lead over Labour plunged from 15 points to six. The same pollsters also found 59% of people thought Mr Cummings should quit.

Six months after his election in 1997, Tony Blair also hit his first big scandal with the Bernie Ecclestone affair, a plain-as-day story about a £1m donation from the F1 boss and F1 coincidentally being exempted from a ban on tobacco advertising. Mr Blair insisted he was a “pretty straight sort of guy”, but it always tainted him.

Mr Johnson blithely absolving Mr Cummings is a similar turning point.

But it is more dangerous. Mr Johnson has never enjoyed great public confidence. He won in December because of Jeremy Corbyn, Brexit fatigue, and by asking Labour voters to lend him their support.

It was also going to be a tightrope to keep the public on side. But now he must walk it with a reputation for treating the rest of us with disdain.

That will seep into every major reform in the years ahead, especially Brexit given Mr Cummings’s pivotal role in the Vote Leave campaign.

A crunch decision in the coming weeks on whether to extend Brexit trade talks with the EU or risk compounding the economic crisis by trading on WTO rules will be an early test.

Mr Johnson’s actions this week have made selling his plans to the country, particularly on Europe and the painful response to the looming recession, immeasurably harder.

He’s got it coming to him.