Sen. Ted Cruz passed Donald Trump in the RealClearPolitics average of Iowa polls on Dec. 12. One would have expected Trump on Dec. 13 to begin questioning whether Cruz’s Canadian birth would make him ineligible to be president. Instead, he waited all the way until the first week of January to begin whispering (by which we mean saying constantly at rallies, on television, and on Twitter) about the “precarity” of Cruz’s situation and the trouble it could bring for the Republican Party if Cruz is its nominee.

And now that it’s happening at long last, well, it’s sort of brilliant.

The question of Cruz’s “natural born citizen” status has been assigned to the catchall category of “birtherism,” but it’s a much different situation than the birther charges against President Obama that Trump spearheaded years ago. The prevailing birther theory held that President Obama was born in Kenya. As evidence for this theory, the birthers had nothing beyond their own stupidity and prejudice. (Typing that, though, will make it likely that I receive hilarious emails about the questionable pixelation on White House uploads of President Obama’s long-form birth certificate. So be it.) In Cruz’s situation, everyone agrees about the facts of Cruz’s birth.

Is Cruz a “natural born citizen” who’s eligible to serve as president? In short: yes. Cruz was born in Canada and lived there until age 4. As two former solicitors general, Neal Katyal and Paul Clement, wrote in an article for the Harvard Law Review in early 2015, “All the sources routinely used to interpret the Constitution confirm that the phrase ‘natural born Citizen’ has a specific meaning: namely, someone who was a U.S. citizen at birth with no need to go through a naturalization proceeding at some later time.” The Congressional Research Service backs up this understanding. And wee baby Ted Cruz was a U.S. citizen at birth. Those born abroad between 1952 and 1986 earned U.S. citizenship at birth if their parents were married and one parent was a U.S. citizen who spent 10 years in the United States with five of those coming after age 14. Cruz’s parents were married, and his mother meets the citizenship requirements.

The only uncertainty about Cruz’s eligibility is that the Supreme Court has never ruled on the meaning of the Constitution’s “natural born citizen” clause. There is a slim possibility that some Democratic goon—hello, Alan Grayson!—could file suit against Cruz’s eligibility, the case could make its way to the Supreme Court, and a majority of justices could, just for kicks, decide that “natural born citizen” does not mean U.S. citizen at birth but something else. I personally rate the chances of this happening at negative 10 trillion percent, since the suit’s success would rely on a ridiculous legal argument and the conservative Supreme Court disqualifying the Republican Party’s presidential nominee.

But it’s that slight, slight chance that Cruz’s eligibility may be imperiled that Trump is sinisterly and shrewdly playing to. He is not running around saying There’s no way that Cruz is eligible!, which is usually how he rolls. He is saying that Cruz has a responsibility to the party to clear himself through the courts in the event he wins the nomination. “How do you run against the Democrat, whoever it may be,” Trump said on CNN Wednesday, “and you have this hanging over your head if they bring a lawsuit?” Trump, bless his heart, is even offering Cruz a remedy through which to prove his eligiblity:

.@SenTedCruz Ted--free legal advice on how to pre-empt the Dems on citizen issue. Go to court now & seek Declaratory Judgment--you will win! — Donald J. Trump (@realDonaldTrump) January 7, 2016

Cruz has been laughing this all off in public. It wouldn’t be surprising, however, if the Cruz campaign is thinking through this more seriously in private. Trump hasn’t put Cruz in a corner just yet but has put him in, shall we say, a spot.

Many Republican primary voters, in large part because of Cruz and Trump’s rhetoric this campaign, are inclined to pick up on and feel unnerved by even the smallest whiffs of foreignness. Recall that Cruz, after news of his dual citizenship came out, renounced his Canadian citizenship in 2014. Why did he do that? I, for one, would love to have the option of a second citizenship in Canada, especially depending on the outcome of the 2016 presidential election. But Cruz perceived his Canadian citizenship as a political liability, and now Trump is reinserting the words Cruz and Canada into the news cycle.

Obviously Republican primary voters aren’t thinking straight about electability concerns just yet, considering that Trump and Cruz are running first and second in most polls. But Republicans want the White House badly after eight years of President Obama and the prospect of even one minute of Hillary Clinton. The fear of something, however improbable, happening to the Republican nominee ahead of the general election and “handing” the race to Clinton is a nagging one.

It’s also worth considering how the rest of the political world has met Trump’s hypothesizing. Cruz has a lot of enemies: his rivals for the nomination, Republicans in Congress, Democrats in Congress … pretty much everyone. All of this is well deserved, because Cruz uses every person and institution around him as a prop for his own personal advancement. When Trump started talking about Cruz’s birth this week, he was not universally condemned, as he usually is when he says something strange. There’s been a surprisingly broad range of actors fanning Trump’s statement.

Sen. Rand Paul, who believes Cruz is a phony who’s stealing his libertarian-leaning votes, first joked in a Fox News Radio interview Thursday, “I think without question [Cruz] is qualified and would make the cut to be prime minister of Canada.” But then: “I’m not an expert on the natural-born clause in the Constitution and people have various opinions. … And we’ve had some previous cases of it, but I don’t think we’ve ever gone through the court system for the Supreme Court to decide one way or another.”

Sen. John “Panama” McCain, who hates every atom in Cruz’s body, joined in on the trolling too, calling the question of Cruz’s eligibility “legitimate.” Ann Coulter, one of the rare figures who’s gone from being a 2012 Romney shill to a 2016 Trump shill, is on a rampage about how Cruz is not a natural born citizen. And don’t expect Democrats to get in the way of Republican “birthers” devouring themselves, either.

Cruz will treat the questions of eligibility as laughable until he can’t, and that point may be coming. Maybe he will end up seeking the declaratory judgment that Trump, ever the pal, has counseled him to seek for his own good. But it would be humiliating, and Trump knows that.

Read more of Slate’s coverage of the GOP primary.