The question many Tories ask this morning will be whether the party’s recent relentless focus on winning over new supporters in traditionally Labor areas in the north is starting to cost them dearly in their southern strongholds.
As always, the reality is more complex.
Chesham and Amersham presented a powerful mix of local and national issues that the Lib Dems were able to capitalize on.
The HS2 rail line runs through the constituency and the proposed planning changes are also a big concern here.
And as the losing Tory candidate said, the Lib Dems threw the kitchen sink, the microwave and everything in that seat.
Tactical voting may also have been at play with the shift from Labor voters to Liberal Democrats to secure a government defeat.
But all that said, this trend – of traditional conservative regions in the south being eaten away by opposition parties – was visible in the results of the local elections in May.
David Cameron’s former Witney constituency in Oxfordshire and Home Counties stronghold Toryism Chipping Norton both won Labor advisers in the vote.
Meanwhile, further south in Sussex, the Tory leader of the Worthing Borough Council has explicitly blamed the focus on leveling in the north and the prevalence of planned property developments in the south for a loss of seats in his area.
The Lib Dems echo this this morning, saying voters in places like Chesham and Amersham are fed up with being taken for granted.
Demographic shifts due to the move of young families from central London, as well as strong support for staying in the EU in 2016 may also have played a role.
The message from Conservative sources this morning is that this is a predictable midterm protest vote against a party that has been in power for ten years and that the seat can be renewed in a general election.
That may be true – but remember, that logic was not confirmed in the Hartlepool by-election where the Tories took the seat in May.
It also comes at a time when the government is conducting good polls, in the midst of a successful vaccine rollout.
All of this means that this is a more surprising result than Hartlepool.
But just because this brick has turned yellow doesn’t mean the whole blue wall is guaranteed to fall.
For starters, there are real questions about whether there is a large enough harvest of seats that the Conservatives would realistically lose in a general election to counter their victories in the north.
Moreover, while in the north, the Conservatives are now seizing the votes of Labor on their own, in the south, the spoils of disillusioned Conservative voters are more frequently shared between several opposition parties.
For Labor, this is bad news.
This by-election saw the opposition vote plummet to just over 600 votes.
May’s bumper ballot also saw good gains for the Green Party, as well as the Lib Dems.
Expect questions for Sir Keir Starmer today on why Labor fails to win in places like Chesham and Amersham when the Lib Dems do.
The practical question for the next general election might be whether anti-conservative election pacts are the only way to come close to removing Boris Johnson from power.
Countless prime ministers have learned the lesson of taking voters for granted the hard way.
It is an irony that has not escaped the Conservatives that the same sense of disillusionment they exchange in the north now seems to be costing them votes in the south.
This is a stunning result for the Lib Dems and while it’s too early to talk about the collapse of the South Blue Wall, it is certainly teetering.