This is how democracies unravel.
Long after the Green Party's victory in the Gorton and Denton by-election has been forgotten, the campaign and the precedent it set will continue to disfigure our politics.
We are Balkanising our country, moving beyond citizenship as our primary political identifier and instead relating to one another as members of antagonistic tribes whose territories happen to overlap.
The Green Party's behaviour in the run-up to yesterday's by-election should place that party beyond the parameters of democratic decency.
Divisive, sectarian and ready to stoke Muslim grievances against Israel and India, the former eco-activists have dropped any pretence of appealing to voters as British citizens.
At one point, their candidate, Hannah Spencer, told her Reform opponent, Matt Goodwin, that the Manchester Arena bomb had happened 'because people like you are dividing people'.
Not that the Greens started it. Jeevun Sandher, a Labour MP of Sikh heritage, complained about the 'dog-whistle' of a Green by-election video in Urdu that featured a picture of Prime Minister Sir Keir Starmer shaking hands with his Indian counterpart Narendra Modi, a deeply unpopular figure in Islamic communities.
It had evidently slipped Sandher's mind that, five years earlier, at a by-election in Yorkshire, Labour did precisely the same thing, running a picture of Boris Johnson with Modi, next to the caption, 'Don't risk a Tory MP who is not on your side'.
The Green Party's behaviour in the run-up to yesterday's vote should place that party beyond the parameters of democratic decency.
Divisive, sectarian and ready to stoke Muslim grievances against Israel and India , the former eco-activists have dropped any pretence of appealing to voters as British citizens.
At one point, Spencer told her Reform opponent, Matt Goodwin (pictured, with party leader Nigel Farage, at a campaign event earlier this month), that the Manchester Arena bomb had happened 'because people like you are dividing people'
Does this really need spelling out? No democracy can flourish if its people lack common identity and shared allegiance.
There have been multi-national regimes down the years - the Habsburgs, the Ottomans, the Soviets - but they survived only for as long as they remained autocratic.
The moment their peoples were given the right to choose, they fractured into their component ethnicities.
What is happening here is vastly more culpable. We have moved from being a cohesive nation, in which almost everyone accepted certain norms - equality before the courts, parliamentary democracy, religious pluralism, free speech - to one in which we ourselves are teaching groups of our own citizens to be separate and resentful.
We might have handled immigration differently, with more manageable numbers. But our real error was to turn our backs on British patriotism.
During the 20th century, most settlers arrived in Britain in positive spirits. People don't abandon their family and language to go to places they despise.
But we taught their children that Britain was rapacious, reprehensible and racist. No wonder some of them turned against the country of their birth.
Labour has long encouraged such a narrative among ethnic minority communities for partisan gain and can hardly complain when others, notably the Greens and the Gaza independents, take it further.
The Greens campaigned largely on two issues: lifting immigration controls and hostility to Israel.
Why those issues? Because they unite what is left of the Greens' previous base, who regard the whole notion of discriminating between citizens and non-citizens as somehow racist, with its new, Muslim voters.
'We've tried to appeal to people from all kinds of backgrounds,' said the Greens' deputy leader, Mothin Ali, when asked about the Urdu video. 'That's about inclusivity.'
An odd word to use for campaigning in a language 19 out of 20 British citizens don't understand.
Not that the Greens started it. Jeevun Sandher, a Labour MP of Sikh heritage, complained about the 'dog-whistle' of a Green campaign video (pictured) in Urdu - but it evidently slipped his mind that, five years earlier, at another by-election, Labour did precisely the same thing
We have moved from being a cohesive nation, in which almost everyone accepted certain norms to one in which we ourselves are teaching groups of our own citizens to be separate and resentful.
Labour has long encouraged a negative narrative about Britain among ethnic minority communities for partisan gain, and can hardly complain when others, notably the Greens and the Gaza independents, take it further.
The Greens campaigned largely on two issues: lifting immigration controls and hostility to Israel, to unite what is left of the Greens' previous base.
'We've tried to appeal to people from all kinds of backgrounds,' said the Greens' deputy leader, Mothin Ali, when asked about the Urdu video.'That's about inclusivity.'
An odd word to use for campaigning in a language 19 out of 20 British citizens don't understand.
Why are Leftists playing this game? Do Greens think that their new voters will buy into the rest of their policies?
Is there an alternative? Yes. Respectable parties should appeal to British Muslims as precisely that: British.
The backlash risks not being a return to civic liberalism and a renewed emphasis on individual rights.
It could also be collectivist and self-pitying but directed the other way around.
The reason the Greens have lost interest in the environment is not just that they would find it hard to outflank Ed Miliband; it is that it doesn't pull in as many votes as campaigning for immigration and against Israel.
What the French call 'Islamo-gauchisme' - Islamo-leftism - is, by its nature, negative.
All that unites the eco-loons with the Islamists is a dislike of the West in general and Israel in particular.
Every such alliance has resulted in the first lot, the white Lefties, being swallowed up by the second.
They should recognise that a lot of Green and Labour voters here support conservative parties in their countries of origin, where their sense of victimhood has not been encouraged.
They should emphasise the values that encouraged millions of British Muslims to volunteer in the two wars.
The best way to defeat a bad idea is with a better idea. And if there is a better idea out there than an open society based on property rights and personal liberty, I have yet to hear it.