Donald Trump is now questioning whether Ted Cruz is eligible to be president, because the Constitution states that the president must be a “natural born Citizen,” and Cruz was born in Canada to an American mother. Trump is even getting some support from John McCain, himself born outside the geographic confines of the U.S., who says he isn’t sure whether Cruz qualifies (the fact that McCain loathes Cruz with every atom of his being couldn’t possibly have anything to do with this).

So what’s really going on here?

Before I answer that question, we should be clear about one thing: there seems to be virtually no debate among constitutional scholars that when the Framers wrote that the president had to be a “natural born citizen,” they didn’t mean that he had to be born within the borders of the United States, but rather someone who was a U.S. citizen from birth (here’s a Constitutional analysis if you want it). Cruz qualifies, just as McCain qualified despite being born on a naval base in the Panama Canal Zone.

And full disclosure requires me to admit that I have a personal sympathy for Cruz on this question, since we share a not-so-secret Canadian shame. Like him, I was born in Canada to an American mother (though my father is Canadian, not Cuban). I will note that I’ve been living in America since I was two years old. Cruz’s family didn’t come south until he was all of 4 years old — though if in those extra two years he was subjected to any Canadian propaganda meant to inculcate the national traits of politeness and modesty, it didn’t seem to take hold. I certainly hope that, as it was with other inspiring trailblazers before him, Cruz’s courage enables other Canadian-Americans-who-are-actually-not-really-Canadian to hold their heads high and believe that they can achieve anything they want with hard work and a faith in the promise of this great land.

With that out of the way, let’s return to the question of what Donald Trump is really up to here. His campaign has a kind of accidental genius about it, and one of the things he does is to throw a whole bunch of stuff up against the wall and see what sticks. When the press focuses in on something controversial he says, whether it’s about one of his opponents or anything else, he runs with it. Since his candidacy is based in large part on fueling and exploiting nativist resentment — against immigrants, against Muslims, against anybody who doesn’t look or talk like you — it was almost inevitable that he’d go after Cruz as alien and threatening once Cruz began to gain strength in the polls.

On a couple of occasions, Trump has tried to question Cruz’s religion by telling Iowa voters (who are heavily evangelical), “You gotta remember, in all fairness, to the best of my knowledge, not too many evangelicals come out of Cuba, okay? Just remember that.” As a political attack, it’s both ineffective and ridiculous. First, what is he saying — that Cruz is lying about being a Southern Baptist, and he’s actually Catholic or something else? No one’s going to believe that, no matter how much they like Trump. Second, Trump himself is not an evangelical, so it’s hard to say “he’s not one of us” when you yourself aren’t part of that particular “us.”

Perhaps that’s why the religion attack got a limited amount of attention, and Trump probably be won’t be bothering with it much in the future. But the birther attack is something else.

There’s a long and shameful history of candidates calling their opponents alien, telling voters they should vote against them because they aren’t “one of us” or don’t share “[insert your state here] values.” Up until now, most of those kinds of sentiments in this race have been coming from Trump, and they haven’t been directed at his opponents. But is anyone really surprised that he’d go after one of the two candidates in race with Hispanic heritage this way?

As powerful as that idea can be in campaigns — suspicion of outsiders and people who are different has been powerful enough to help Trump to the top of the polls — it may not have much of an effect on how Republican voters think of Ted Cruz. That’s because Cruz neither conveys, nor by all appearances feels, a particularly strong Hispanic identity.

I want to make perfectly clear that this isn’t a criticism, it’s just who Cruz is. If he “read” more Hispanic, it would be more complicated, since today’s Republican Party is simultaneously eager to reach out to Hispanic voters and held back by a deep suspicion and anger toward immigrants among significant parts of its base. In any case, Cruz wasn’t raised in a heavily immigrant milieu, he doesn’t speak fluent Spanish, he doesn’t toss in Spanish sentences when he’s speaking to an audience that might understand them (like Jeb Bush does), and he doesn’t wax rhapsodic about Cuban food (like Bush does about Mexican food).

It isn’t that Cruz is trying to hide anything; it’s just that the Cuban part of his heritage just doesn’t seem to be an essential part of his daily life and history. When you combine that with his extremely hard line on immigration (like Trump, he wants to build a wall across the entire southern border), despite his last name and however he actually conceives of his own personal identity, to many voters Ted Cruz probably won’t really seem all that Hispanic.

But you know who does? Marco Rubio. Rubio was raised in an immigrant milieu, he does speak fluent Spanish, and he often talks about the struggles of his immigrant parents as a way of framing his own personal story. So here’s a prediction: if Rubio starts to rise in the polls and Donald Trump begins to see him as a serious threat, Trump is going to find a way to say to Republican voters, “Look at this guy — he’s not one of us.” It will be attention-grabbing, even appalling. The news media will be drawn inexorably to it. They’ll host lots of discussions about whether the GOP is ruining its chances among Hispanic voters.

It may be that if Trump does that, it won’t make a difference, because anyone predisposed to vote against Marco Rubio because of his ethnicity is already in Trump’s camp. But it isn’t going to be pleasant to watch. For now, though, Trump’s target in this regard is Cruz.