Black Lives Matter came up with the single most effective political slogan of the year.

While no one was likely to be overly impressed with Joe Biden’s line, “Build Back Better,” and Donald Trump’s “Keep America Great” or “Make America Great Again, Again” didn’t have the resonance of the original 2016 version, BLM broke through the clutter with a catchphrase that was memorable, pungent — and utterly devastating to Democrats.

After a surprising Tory victory in the British parliamentary election in 1992, the pro-Tory tabloid The Sun famously boasted, “It’s the Sun Wot Won It.” In the same spirit, it could be said that in this year’s congressional election, “It’s ‘Defund the Police’ Wot Lost It.”

Democrats have an uphill battle to take the U.S. Senate — pending two Georgia run-offs — and suffered shocking setbacks in the House that drastically diminished their majority.

All over the map, Democrats got hammered on defunding the police, which couldn’t have been better designed to extract maximum political pain with zero upside.

Black Lives Matter has been a stunning success in the elite culture. It won the obeisance of almost every major institution, from corporate America to sports leagues to colleges. It created a powerful, if dishonest, narrative of systemic police racism. It got invested with nearly a holy significance, such that criticizing it is considered at least a sin and perhaps a firing offense.

Much more importantly, at least for a time after the death of George Floyd in police custody in Minneapolis, it won the goodwill of a clear majority of Americans.

To take this position of strength and use it primarily to associate your allies with a politically radioactive position requires extraordinary strategic folly and heedless ideological fanaticism. BLM had both, in ample supply.

The notion of defunding the police had been rattling around the left for a long time, but the George Floyd protests took it mainstream. BLM leaders touted the idea and scolded Democrats for not getting on board (“Read the room,” one implored, “People are calling for defunding the police”). Activists painted the slogan on a street leading to the White House. BLM pushed municipalities to actually act on the proposal.

Whenever someone tried to take the edge off defunding the police by redefining it as simply reallocating some law-enforcement dollars, defenders piped up to say, No, we really mean it. Alexandria Ocasio-Cortez balked at a proposal to cut $1 billion in police funding in New York City: “Defunding the police means defunding the police.” The New York Times ran an op-ed against incrementalist interpretations, “Yes, We Mean Literally Abolish the Police.”

Predictably, Republicans took the weapon handed to them and used it, as Democrats would have done if a voluble faction on the right called for, say, abolishing child welfare agencies.

The effectiveness of the attack now has Democrats who are otherwise loath to speak ill of BLM complaining about what its catchy slogan did to the party.

The consequences have been even worse in riot-plagued Minneapolis. The city council took BLM not only seriously, but literally. It absurdly vowed to defund an already demoralized and overwhelmed police force. The city has been suffering an ongoing crime wave, with shootings of Black victims skyrocketing as police struggle to respond.

After support for BLM surged last spring, positive feelings for it have been declining. A Pew Research report showed support for BLM dropping from 67% in June to 55% in September. Only 45% of white people expressed support for the movement.

Given that BLM elevated the dumbest, most self-destructive slogan in American politics in a very long time, and an even more atrocious policy, its numbers deserve to fall further. Advocates of defunding the police argued that setting out an extreme position could have a political effect even if it had no chance of enactment.

They proved exactly right — just not how they expected.