Getty ImagesThere are so many implications of the Gorton and Denton by-election that are essential to understand, but it's best first to dwell on the winner: the Greens.
The closest they had come to winning a Westminster by-election before was in 2023 in a seat in Somerset where they got about 10% of the vote and finished third.
Blasting away one of Labour's biggest majorities shows that under the more left-populist leadership of Zack Polanski, the Greens are now playing in a different political league.
Polanski and the party's new MP, Hannah Spencer, were explicit that they do not see this as a self-contained local contest but as the blueprint for all sorts of other parts of the country.
The fear among plenty of Labour MPs is that they are right.
Labour politicians have over the past year or so become comfortable with the idea that Reform UK could usurp the Conservatives as the main force on the right of British politics.
Now they are confronted with the niggling possibility that something similar could be happening on their side of the political spectrum too.
It is much too soon to assert that this is likely or even plausible.
But it certainly is possible, and that is part of the reason why this by-election may linger long in the memory.
As it stands - and that is an important caveat - there are no signs that result in Greater Manchester will precipitate another Labour leadership wobble in the immediate term.
Even a Labour MP who messaged me about Sir Keir Starmer in the aftermath of the result simply saying "time to go" took the view that any change should happen after the May elections rather than now.
Nevertheless, the call from Angela Rayner, Sir Keir's former deputy, for Labour to take this as a "wake up call" and become "braver" was notably forthright.
A word about the Conservatives.
Gorton and Denton was not their natural terrain and tactical voting was rife, but even so getting just 700 or so votes and losing their deposit is a bleak omen.
The party which was in government less than two years ago ended up about 14,000 votes behind the winner and only 547 votes ahead of the Official Monster Raving Loony Party's "Sir Oink A-Lot".
It's worth remembering that this is the second by-election since the 2024 general election.
Last May in Runcorn and Helsby, Labour were also beaten by a non-traditional insurgent force: in that case, Reform.
Yes, it is fairly typical for governing parties to get a kicking in by-elections.
But taken together, along with the Conservatives' political no-shows in both contests, these by-elections point to a new dynamic of surging political forces to the traditional parties' left and right.
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