(CNN) Donald Trump ought to keep a close eye on Britain's vote Thursday on whether to leave the European Union.
The so-called Brexit has turned into a referendum on British identity, a debate about sovereignty and immigration that taps into all of Trump's major themes. As such, the outcome will likely reveal the potential and the limits of angry conservatism -- the kind of conservatism that repulses at least as much as it excites.
The EU is not a left/right issue in Britain. Support and opposition cuts across traditional partisanships. The basic arguments are these: the "Remain" camp believes a little democracy is worth sacrificing to be part of the European single market, while "Leave" believes Britain doesn't get enough out of the bargain to justify being governed by foreign bureaucrats.
When the campaign officially began in April, Remain organizers had a clear advantage. They rolled out one expert after another to argue that leaving the EU would trigger a recession and give courage to the West's enemies. Even Barack Obama said that Britain would go to "the back of the queue" when it came to seeking trade deals.
But even as Remain added big name endorsements to its ranks, it created an impression that the pro-EU position wasn't a campaign so much as a conspiracy -- and a pretty desperate one at that. Prime Minister David Cameron even implied that leaving the EU might lead to war. Remain started to look not authoritative but desperate.
"Leave" cleverly let Remain exhaust itself. Then it hit back. It argued that Britain couldn't control its borders so long as it is a member of the EU, and that Brexit would allow the government to shut the door to cheap European workers. This was the equivalent of Trump's promise to build a wall along the Mexican border -- and it worked. Leave surged in the polls. Studies showed that those who thought the referendum was about the economy still backed Remain. Those who thought it was about immigration were coalescing around Leave.
There are enormous differences between Leave and Trump. Leave does contain long-time politicians who absurdly pretend to be, in one ex-government minister's words, part of a "peasants revolt." But Leave doesn't do Republican-style religious conservatism and is divided over the role that immigration should play in its strategy; some would prefer not to talk about it at all.
Leave is articulate where Trump is simply verbose: the movement's effective leader, former London mayor Boris Johnson, is a scholar of the classics.
There are, however, similarities. Leave gives the impression of promising less immigration. Leave wants to put the interests of the British people first, which has led others to accuse it of nativism. And, most important, its coalition is Trump-ish in character. It combines ordinarily Left-wing working-class Britons who feel oppressed by globalization, middle-class Right-wing patriots, and a sprinkling of mega-wealthy businessmen -- all united by a profound belief that whatever they might be, they are definitely not the establishment.
This is a populist conservative revolt among people who feel they have been misled and misruled for too long. They are skeptical of experts, because they've so often been wrong, and immune to warnings of economic risk because they have lived with risk their entire lives.
The depressing nature of their circumstances calls to mind the lyrics of "Me and Bobby McGee": "Freedom's just another word for nothin' left to lose. Nothin' ain't worth nothin' but it's free."
If you've got very little money, all you do have is your country -- and you sure as hell aren't going to let the EU take it away from you. "We want our country back" cry some of the Leave posters.
For a few weeks, it seemed as if there were enough of these angry people around to win the referendum. But then, last Thursday, a gunman murdered a member of Parliament. And the whole nature of the campaign changed.
No one is suggesting a direct line of causality between the Leave campaign's rhetoric and the death of Jo Cox. But many voters will infer one. Cox was a liberally minded, pro-EU MP; her attacker is alleged to have associations with the far-Right.
The very morning of the assassination, one unofficial leader of the Leave camp had unveiled an anti-migrant poster that many found to be distasteful. At worst, some have suggested that Leave has contributed to a tense and ugly debate about Britishness that fosters extremism. And voters may well subconsciously associate the heady success of Leave with a brutal killing -- suggesting that a Leave vote is a vote for chaos.
This is probably why Trump's polls have not been so good this summer either. His fight with a judge of Mexican heritage and his blustering response to the Orlando tragedy have shown that he's not prepared to temper his furious style.
Populist conservatism is fine for a primary season, when it's about registering discontent. To send a message to the powerful, sometimes you have to shout. But as we've moved towards the general election phase, the idea of Trump the candidate becoming Trump the President causes one to stop shouting and think: We know what he is against but what is he for? And while he might not be responsible for the violence at his rallies, do we want that violence in the White House?
This is the problem now bedeviling Leave. It has to win undecideds who, by their very nature, lack the passion to be willing to join a holy crusade.
The EU referendum has proven that a constituency for anti-establishment anger exists in Britain. On Thursday we shall discover if it has a majority.
I shall be voting for Leave: I believe the EU is incompetent and that Britain should decide its own laws. But I'll cast my ballot suspecting that what made the Leave movement possible is what might also, at the last minute, defeat it. Too much fire, too much heat.
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