If you’re worried about the effect Donald Trump’s brand of xenophobic populism is having on America, you should be paying attention to what’s going on in Britain right now.

On Thursday, Jo Cox, a 41-year-old rising star in Parliament who was known for her support for Syrian refugees, was murdered by one of her constituents. And while police are still investigating the murder and early reports aren’t always reliable, there appears to be evidence from multiple sources that her attacker had ties to right-wing nationalist politics.

Cox was murdered less than a week before Britain is set to vote on whether or not to stay in the EU. The "Brexit" campaign has gotten extremely vicious, and supporters of leaving the EU have, increasingly, catered to nationalist fears of immigrants to make their point. In the midst of that, Cox’s murder hasn’t just been a tragedy (both sides suspended campaigning yesterday) — it’s been something of a wake-up call to many observers.

Alex Massie, a columnist for the Spectator (a conservative British magazine), wrote a beautiful column in the wake of Cox’s murder. Massie explains, better than any commentator I’ve read, the relationship between apocalyptic rhetoric and panic-induced violence:

When you encourage rage you cannot then feign surprise when people become enraged. You cannot turn around and say, ‘Mate, you weren’t supposed to take it so seriously. It’s just a game, just a ploy, a strategy for winning votes.’ When you shout BREAKING POINT over and over again, you don’t get to be surprised when someone breaks. When you present politics as a matter of life and death, as a question of national survival, don’t be surprised if someone takes you at your word. You didn’t make them do it, no, but you didn’t do much to stop it either. Sometimes rhetoric has consequences. If you spend days, weeks, months, years telling people they are under threat, that their country has been stolen from them, that they have been betrayed and sold down the river, that their birthright has been pilfered, that their problem is they’re too slow to realise any of this is happening, that their problem is they’re not sufficiently mad as hell, then at some point, in some place, something or someone is going to snap. And then something terrible is going to happen. We can’t control the weather but, in politics, we can control the climate in which the weather happens.

The climate in which Cox was killed: "put our own people first"

In this case, we still don’t know what, exactly, caused "the weather" — that is, Cox’s murder.

A suspect has been arrested. Early reports — which, remember, aren’t always reliable — indicate a past of mental-health issues, but also ties to neo-Nazi groups in the US and right-wing groups in the UK. Two named eyewitnesses to Cox’s murder have claimed that her attacker shouted "Britain first!" as he shot and stabbed her (though others dispute this claim).

But whether or not Jo Cox was murdered as an act of right-wing terrorism, UK politics has reached a point where it wouldn’t be surprising to see something like that happen. That is notable in itself: It’s the "climate" in which the "weather" took place.

Cox had been targeted with "malicious communications" from a different constituent earlier this spring. After the murder, local police have launched an investigation of one far-right group after it posted a tweet celebrating Cox’s death. And another member of Parliament has confirmed that his office got a death threat Wednesday, as part of a wave of "homophobic and racist remarks."

The face of right-wing politics during the Brexit campaign has been Nigel Farage, the leader of the UK Independence Party. UKIP, as it’s known, is the main right-wing party in Britain — which, like a lot of right-wing parties in Europe, has gained power and visibility thanks to the backlash over refugees entering the continent.

Farage believes leaving the EU is a matter of life or death for Britain — he feels Britain is under threat by "mass immigration," and that the country won’t be able to restrict it while it’s still in the EU. (This may remind you of someone.)

He’s claimed Britain will be "flattened" if it stays in the EU and accused Prime Minister David Cameron of putting other countries ahead of his own. (This may remind you of someone.)

As Farage put it during a legislative debate last week, "My priority would be, we put our own people first. It is about time we did." (This may remind you of someone.)

The conservative establishment in Britain isn’t quite on board with that anti-immigrant messaging — the organization officially leading the pro-Brexit side of the current debate has tried to focus instead on national sovereignty and trade.

But despite their best efforts, immigration has ended up being the central issue of the Brexit debate. Farage won the messaging wars, and he’s become one of the most visible supporters of the "leave" campaign.

And the closer the Brexit vote comes, the more aggressive his rhetoric has gotten. (This may remind you of someone.)

On Thursday morning, shortly before Cox’s murder, Farage unveiled a billboard depicting a horde of "foreign"-looking immigrants — implying they would overrun Britain if it stayed in the EU.

(This may remind you of someone.)

The left-wing New Statesman described it as reminiscent of "Nazi propaganda."

In May, he suggested that Britons’ anger over migration "could lead to violence."

This, too, may remind you of someone.

"Nigel Farage isn’t responsible for Jo Cox’s murder," Alex Massie wrote yesterday. That’s entirely correct — to borrow Massie’s analogy, politicians like Farage and Trump don’t control the weather. But they do partly control the climate.