The North Shropshire seat flipped from a 23,000 Conservative majority to a 6,000 Liberal Democrat win. In private, Johnson's lawmakers are talking seriously about how long he can carry on as UK Prime Minister. They are worried this result shows voters are catching onto the idea of tactical voting and that Johnson's ability to lock down Brexit voters might have waned.

The loss comes in the same week that Johnson's own MPs openly defied him by voting against new Covid measures in parliament. Some 99 Conservatives defied the PM.

The election in North Shropshire, in central England, only took place because of a catastrophic own goal by the Prime Minister. Last month, Johnson whipped Conservative Members of Parliament to vote on an amendment that would overturn the 30-day suspension of their colleague Owen Paterson.

Boris Johnson was criticized for failing to wear a mask on a visit to a hospital in Hexham, Northumbria, northern England, in November.

Paterson had been founding guilty of breaching lobbying rules, personally contacting government ministers on behalf of companies that paid him an amount that totaled £100,000 ($136,000).

After days of fury from people all over the political divide, Paterson resigned his North Shropshire seat. Between Paterson's resignation and Thursday's by-election, Johnson has been drowning in scandals that have wrecked his poll numbers and posed serious questions about his leadership.

Johnson has spent the past two weeks fighting off allegations that he and his associates held illegal parties in Downing Street while the rest of the country was in varying degrees of lockdown. The Prime Minister has insisted that he believes no rules were broken, and has asked one of his top civil servants to investigate the alleged parties.

Prior to that, he had been dogged by accusations that he accepted improper donations to fund a renovation, while his government has been accused of handing lucrative Covid contracts to people with links to the Conservative party. Johnson's spokesman has insisted he has "acted in accordance with the rules at all times."

Johnson stands alongside Chief Scientific Adviser Patrick Vallance during a press conference after cases of the new Covid-19 variant were confirmed in the UK on November 27.

Suffice to say, all of this is a stark turnaround for a man who won a landslide election just two years ago. And it's no surprise that figures within the party are now talking seriously about removing Johnson from power.

The Conservative Party was never in love with Johnson as such. He took over as leader of the party and the country because his predecessor, Theresa May, had run out of road and couldn't deliver Brexit.

Conservative MPs had resisted a Johnson leadership campaign in the past. He was seen as a showman and a fantastic cheerleader, but fundamentally too chaotic and untrustworthy to lead.

Brexit changed everything. In 2019, Conservative MPs held their noses and did a deal with Johnson: Get Brexit over the line and win us an election. Johnson did both things and consequently was given the keys to the car, and allowed to drive it however he liked.

That was all well and good while he looked bulletproof. But Conservatives are now worried the PM is so weighed down with scandals and sleaze, he has passed a point of no return. They also fear that 2022 will be harder than 2021.

The Omicron variant peak will pass and the economic, societal and public health consequences of another Christmas wrecked by Covid will be impossible to ignore. Johnson will be the face of these issues and the blame will rest squarely on him.

"He goes into the new year with problems piling up. The cost of living will rise, there might be supply chain shortages. And he's facing all these problems with no ideological base or friends in the party," says a former senior cabinet minister.

"He has a finite window to improve -- but few believe he will seize it," says a senior MP.

Pictures obtained by The Mirror show photos of Johnson hosting a Christmas quiz party at 10 Downing Street last year.

If Johnson's number really is up, removing him from office will be extremely painful and difficult to negotiate. Calling a vote in his leadership now will be very hard. As the former cabinet minister pointed out, "local associations tend to be loyal to leaders," which will make it hard for their MPs to call for Johnson's head.

A botched leadership challenge would mean Johnson is immune from another challenge for 12 months -- and it seems most unlikely he would resign in that time.

The second, arguably more important issue, is who might replace him? There are other popular cabinet ministers who clearly have leadership ambitions. But given how difficult 2022 looks, who on earth would want to take the poisoned chalice?

However, the longer he remains in office, the more likely it is he stays for the next scheduled election in 2024. If recent polls are to be believed, that election could see the Conservatives lose a lot of seats.

It's surreal that as recently as October, Johnson seemed untouchable. No matter what happened -- fuel shortages, huge Covid numbers, people drowning in the English Channel -- his polling numbers remained strong enough to win an election.

The past two weeks might be an indication that the magic has started to wear off. And if that's the case, Conservatives will have to find some way of silencing their head cheerleader who has suddenly become the least popular kid in class.