Republican primary front-runner Donald Trump on Sunday said he’s “not sure” whether primary rival Marco Rubio can run for president.

Trump on Saturday retweeted a follower who said the Florida senator, who was born in Florida to Cuban parents, is not eligible to run for higher office.

“I think the lawyers have to determine it,” Trump said on ABC’s “This Week,” when asked if he believed the tweet. “It was a retweet. Not so much with Marco, I’m not really that familiar with Marco’s circumstance.”

When pressed on why he retweeted the claim if he wasn’t sure about it, Trump said he was trying to “start dialogue” about the issue.

“Uh, because I’m not sure,” he said. “I mean, let people make their own determination.”

“Somebody said he’s not, and I retweeted it,” he added. “I have 14 million people between Twitter and Facebook and Instagram, and I retweet things and we start dialogue and it’s very interesting.”

Trump has also questioned the eligibility of primary rival Ted Cruz, who was born in Canada to an American mother.