Brand new year, brand new resurgence of one of the more frustrating and futile political firedrills out there: Ted Cruz birtherism.

The ringleader is—shockingly!—Donald Trump, who reopened the old controversy about whether Cruz is eligible to be president, given that he was born in Canada, in an interview with The Washington Post:

Republicans are going to have to ask themselves the question: “Do we want a candidate who could be tied up in court for two years?” That’d be a big problem. It’d be a very precarious one for Republicans because he’d be running and the courts may take a long time to make a decision. You don’t want to be running and have that kind of thing over your head .… I’d hate to see something like that get in his way. But a lot of people are talking about it and I know that even some states are looking at it very strongly, the fact that he was born in Canada and he has had a double passport.

To get a few things out of the way: First, it is not true that Cruz “has had a double passport.” There’s no such thing—though Cruz was a dual citizen, apparently unwittingly, for years before renouncing his Canadian citizenship in 2014—and Cruz says he never held a Canadian passport.

Second, and more importantly, the premise is false, as I explained in detail in 2013: Because Cruz’s mother was an American citizen, Cruz is a natural-born United States citizen from birth, regardless of what other citizenships he may have held. It’s not worth relitigating that question, but it is worth discussing why Trump might be bringing it up, why others are joining in, and what it means for the election.

Trump isn’t the only one in on the carnival. With the issue on the table again, other politicians are joining. Cruz and Trump’s presidential rival Rand Paul quipped, “You know, I think without question he is qualified and would make the cut to be prime minister of Canada, absolutely without question, he is qualified and he meets the qualifications.” John McCain—the senator and former presidential candidate who was born in Panama, where his father was serving at an American base in the Canal Zone—was asked about it too, and replied, “I think there is a question. I'm not a constitutional scholar on that, but I think it's worth looking into. I don't think it's illegitimate to look into it.” (He added: “I know it came up in my race because I was born in Panama, but I was born in the Canal Zone, which is a territory.”) Representative Nancy Pelosi, the Democratic minority leader, responded to a question by saying she could see a difference between McCain and the Canal Zone on one hand and Cruz and Canada on the other.

All three of these politicians are probably trolling. McCain has shown little patience for birtherism in the past—he famously rebuked a questioner who called Barack Obama an “Arab” during a 2008 campaign stop—but he has even less patience for Ted Cruz. Paul may profit from taking a shot at a fellow candidate, but he also loves to troll, as McKay Coppins documents in The Wilderness. And Pelosi, too, is an accomplished troll.

Trump reemerged as a political force on the basis of his own championing of birtherism in 2011; he allegedly bankrolled investigators who he sent to Hawaii to look into Obama’s origins, though he never released the results. Even since Obama released his long-form birth certificate, as Trump demanded, Trump has quietly continued to espouse birtherism. Given all that, it would be hard for him to not at least go through some motions on questioning Cruz’s eligibility—even if Obama had been born abroad, his mother was an American citizen, which would give him the same claim to citizenship that Cruz does. (Not that Trump has allowed a foolish consistency to be the hobgoblin of his “really smart” mind.)

Moreover, the birther attack gives Trump a good method to attack Cruz, who has recently emerged as his major rival in polling both nationally and in Iowa. But what kind of weapon is birtherism? It is, at its root, an effective way of telling voters that Cruz isn’t like them. That he’s not one of us. That he’s different. In other words, it capitalizes on all of the anti-immigrant, anti-foreigner sentiments that have driven his campaign all along.

Given the overwhelming evidence of Obama’s birth in Hawaii—the birth certificates, the newspaper notices, the lack of any contradictory information—Obama-focused birtherism was always essentially about a reminder that Obama was different: someone of mixed race, who grew up partly overseas. Simply asserting that Obama was black was socially rejected as baldly racist, but questioning whether he was really an American (and whether he might just be a Muslim) were ways of pointing to his difference. Polls showed strong overlap between people who believed Obama wasn’t an American and racial prejudice. A study found connections between racism and perception of Obama as un-American.

And don’t the questions about Cruz—and hey, he’s just asking questions folks; wouldn’t it be a shame if his presidency was tied up in red tape for two years, even if he's eligible?—function in just the same way? “Basically the only people who believed the birther claims against Obama were GOP primary voters,” Obama’s former communications director Dan Pfeiffer, argued on Twitter. “Cruz should not take this lightly.” Any time a Democratic operative is giving advice to Republican candidates, candidates should take it with a giant grain of salt. But Pfeiffer may have a point here. Although there were some Democrats who believed the birther attack, it was most potent among Republican primary voters—and not all Republican primary voters, but a particular subset.

Cruz positioned himself for months as someone similar to Trump, in the hopes that when Trump imploded (as was widely expected), he could take over Trump’s voters. Instead, Cruz has risen while Trump stays high, which means they’re still fighting for those voters. The very particular subset of voters who were susceptible to birtherism are likely also sympathetic to Trump. Emphasizing Cruz’s otherness is a good way to keep them in his camp.

The birther insinuations aren’t the only Trump line that achieves this. Take one of his first sorties against Cruz, in mid-December. “I do like Ted Cruz, but not a lot of evangelicals come out of Cuba," he said in Des Moines. “Not a lot come out.” On face, this is absurd: Trump has made a few gestures toward establishing his faith, but Cruz has made it central to his political identity. Besides, Cruz’s connection to Cuba is through is father—who happens to be an outspoken evangelical minister. Yet Trump repeated the idea on Face the Nation: “Cuba, generally speaking, is a Catholic country. And you don't equate evangelicals with Cuba. I don’t.” But if these jabs are interpreted mostly as a method of reminding people that Cruz is Cuban, they make a great deal more sense. (Of course, Catholicism has also been used to other people in American politics for centuries.)

The fact that the attacks play into a xenophobic or racist mentality is why it’s unwise for otherwise somber politicians like Pelosi or McCain to encourage them, whatever their motivations. (Brendan Nyhan has shown that even debunking falsehoods can simply reinforce them—to say nothing of the effects of feeding them.)

It’s too soon to know whether or not this tactic will resonate with voters to Cruz’s detriment and Trump’s gain. Major media outlets have so far treated Trump’s questions largely as political theater, rather than as any serious challenge to Cruz’s candidacy. Cruz also benefits from presenting as an average white guy, which makes it harder to stoke racism. And while some Republican primary voters may have bought into Obama birtherism, their belief was surely in some measure motivated by partisanship—if he hadn’t been a Democrat, they wouldn’t really have been interested in the question. Until there’s evidence that these attacks aren’t hurting Cruz, however, you can probably expect to hear more reminders from Trump about how Cruz is, well, different.