Donald Trump — who has been using presidential politics as a stage for his PR stunts for decades — is getting an early jump on 2016, exploiting the fact that at least some in the Republican Party still take his potential candidacy seriously.

The self-proclaimed billionaire made his first political trip to Iowa to speak at the Family Leader event from the same podium as 2012 Iowa Caucus winner Rick Santorum, Senator Ted Cruz (R-TX), and Cruz’s father Rafael, who declared that “homosexual marriage” is a socialist plot.

On the same visit, ABC’s Jonathan Karl gave Trump the chance to back away from the birther claims the “Donald” built much of his 2012 buzz upon.

Trump refused to do so.

“Was there a birth certificate?” he asked. “You tell me. Some people say that was not his birth certificate. I’m saying I don’t know. Nobody knows. And you don’t know, either, Jonathan. You’re a smart guy, you don’t know, either.”

Trump also proved that his birtherism is bipartisan by questioning the eligibility of Senator Ted Cruz to run for president.

“If he was born in Canada, then perhaps not,” Trump said. “That will be ironed out. I don’t know the circumstances. If he says he was born in Canada, that’s his thing.”

It’s almost as if Trump is willing to question the citizenship of any non-white candidate.

Cruz’s mother was a citizen, as was Obama’s, which means both were natural born citizens, making any sort of doubts about either’s eligibility ridiculous.

But Republicans should be on notice that Trump is willing to play the birther card, with all its fraught racial implications, even against their own candidates.