On Thursday, Britain will vote on whether to exit the European Union.

Supporters of the secession movement, known as the Leave campaign, or “Brexit,” think a departure from the EU is necessary to protect the nation’s culture, which they see as vulnerable to the social and political influence of immigration. Opponents say Brexit is an intolerant, nativist contradiction of the democratic spirit of the country.

Brexit, as a measure to separate Britain from newcomers waged during the turmoil of the Syrian refugee crisis, is the other side of the coin Donald Trump as flipped in America. Huge segments of both countries’ respective right wings are turning to exclusionary measures in ill-fated efforts to restore some kind of remembered golden age that likely never existed. But that nostalgia isn’t much more than a thin veneer to hide the nativism underneath both campaigns.

Both movements have incited violence. In America, Trump’s trademark, xenophobic policies have stirred a frenzy of nationalism that frequently boils over in attacks on protestors who, in turn, have attacked Trump-supporters. And in Britain, last week’s bloodcurdling, public murder of politician Jo Cox by a white nationalist revealed the darkest virulence of nativist sentiment.

Cox, 41, was a passionate supporter of refugee rights who opposed Brexit. As the New York Timesobserved, in Cox’s maiden speech to Parliament, delivered last year, she said immigration had “deeply enhanced” her electoral district. “While we celebrate our diversity,” Cox said, “what surprises me time and time again as I travel around the constituency is that we are far more united and have far more in common with each other than things that divide us.”

CNN reports the man charged with her killing, Tommy Mair, shot and repeatedly stabbed the Labour MP while saying something along the lines of, “Britain first, keep Britain independent, Britain always comes first, this is for Britain.”

Once arrested, when asked his name in court, Mair said, “My name is death to traitors, freedom for Britain.”

Mair has been linked to the white-power movement in Britain. Police found Nazi regalia and extreme-right literature in his home, and receipts obtained by the Southern Poverty Law Center indicate Mair purchased the neo-Nazi book “Ich Kampfe” in 1999, and in 2013 subscribed to National Vanguard, a publication of the U.S.-based white supremacist organization National Alliance. In the 1980s Mair also subscribed to a pro-apartheid magazine published in South Africa.

In America, it didn’t take a murder to definitively link Trump to white racism. Rather, the association presented itself in the endorsements that Trump rejects but can’t avoid. Trump might not be running on a “white power ticket,” but the fact remains that his dog-whistle-turned-bullhorn campaign has invoked an ethnocentric spirit determined to cast away “the other” that is allegedly polluting society. And Brexit is the same.

As Politico noted, during a March 7 speech in Madison, Miss., Trump claimed immigrants had “shut Christianity down” — though, according to Pew Research Center, seven in 10 Americans identify as Christian. Calling the immigration situation “completely out of control,” the presumptive GOP nominee has vowed to “take our country back,” but, as Forbes observes, Mexican immigration has been declining for years. Pew reports the number of unauthorized Mexican immigrants living in the U.S. declined by 1 million from the 6.9 million peak in 2007 to 5.9 million in 2012. Since 2010, when U.S. net migration from Mexico hit zero, more Mexicans have left the country than arrived here.

There is also the notion that illegal immigrants don’t pay taxes but enjoy benefits provided by U.S. citizens. In November, speaking to CNN’s Erin Burnett, Trump said “some probably do,” but “only because the employers are insisting on it. But there’s very little, percentage-wise. There’s very little. Probably 5 percent, 10 percent. It’s a very small amount [who] pay taxes.”

This is untrue. Research from the Institute on Taxation & Economic Policy determined illegal immigrants in the U.S. annually contribute about $12 billion to state and local taxes in the form of property, income, sales or excise taxes.

Meg Wiehe, state tax policy director for the Institute on Taxation & Economic Policy, told U.S. News & World Report, “Regardless of the politically contentious nature of immigration reform, the data show undocumented immigrants greatly contribute to our nation’s economy, not just in labor but also with tax dollars.”

According to the institute’s report, roughly a third of immigrants are homeowners, obligated to pay property taxes, an additional 50 percent are thought to pay income taxes, and 75 percent are believed to contribute to social security — benefits that undocumented people are ineligible to receive.

In the UK, fewer migrants receive benefits than in the United States, but the Vote Leave camp — which supports Brexit — shares the misconception of Trump’s supporters in America: that immigrants exploit the country’s welfare system. But they don’t. The Independent reports HMRC (the UK’s tax authority) numbers show since 2012, EU migrants who arrived in Britain paid £2.5 billion more in income tax and national insurance than they received in tax credits and child benefit.

The Leave campaign is fueled by other baseless claims, such as the threat to employment opportunities posed by an unending wave of immigrants.

Iain Duncan Smith, a former work and pensions secretary, and a Leave campaigner, has said increased EU migration forces British workers to compete for jobs with millions from other countries. And indeed, the number of EU workers in the UK has sharply risen by 700,000 since 2013, but this increase paralleled the addition of one million British people to the workforce. As The Independent notes, in an obvious sense, more people has meant greater demand, which creates jobs and stimulates the economy. The argument to leave the EU is not reinforced by the numbers, which casts doubt on the logic behind Brexit, and reveals the fear at the heart of the movement.

This realization has led at least one Conservative politician, who was backing Brexit, to reverse course. In an interview with The Guardian, Saveeda Warsi wondered what kind of impact leave campaigners were having on the country.

“The vision that the Brexit campaign is presenting is not the vision that me and other Brexiters started off with a year ago,” Warsi said. “The ‘hello world’ approach to Brexit, which is open-minded, visionary, inclusive, has been lost. The moderate message has been lost.”

“And instead we have reverted to a campaign that says: ‘The Turks are coming, the Syrians are coming, the refugees are coming, the Muslims are coming, the terrorists are coming.’”

Prime Minister David Cameron has charged Brexit supporters with inciting intolerance with divisive warning about the perils of immigration. Cameron told the Guardian the Leave campaign has “become very narrowly focused” on immigration.

“I’ve always believed that we have to be able to discuss and to debate immigration,” he said. “But I’ve always believed that this is an issue that needs careful handling.”

“We are talking to a country that has a lot of people who have fled persecution and contribute a massive amount to our country. It does need great care.”

Photo: A Brexit supporter holds a Union Flag at a Vote Leave rally in London, Britain June 4, 2016. REUTERS/Neil Hall