To quote Ronald Reagan, “There he goes again.”

After threatening to sue Ted Cruz over his eligibility to run for president because of his Canadian birth (even though Cruz’s mom was and is a natural born American citizen), Donald Trump is now saying he’s “not sure” about Marco Rubio’s eligibility either. Rubio was born in the United States to Cuban immigrants and has lived here all his life, something not even Trump is questioning. And it’s the long established view of Constitutional scholars being born and raised and America makes one a natural-born US citizen. But that hasn’t stopped Trump from trying to gin up doubts about whether Rubio is American enough to be president.

It began Saturday morning when Trump retweeted a follower’s message, which includes a video arguing that neither Cruz nor Rubio are eligible to be president. As expected, Trump was asked about it Sunday and Trump said he wanted to “start a dialogue” about the issue.

"@ResisTyr: Mr.Trump…BOTH Cruz AND Rubio are ineligible to be POTUS! It's a SLAM DUNK CASE!! Check it! https://t.co/NjqWP0pP6X"

— Donald J. Trump (@realDonaldTrump) February 20, 2016

The GOP front-runner was asked by George Stephanoplous on ABC’s This Week if he believed the tweet. “I don’t know,” he said, adding, “I think the lawyers have to determine that.” They generally have. Rubio was born in the United States, but his parents were both Cuban-born and neither was yet a U.S. citizen. Some try to argue that the phrase “natural-born citizen” in the Constitution requires a candidate’s father to be a citizen.

Trump was pressed on why he’d retweet something he wasn’t sure about. He replied, “Because I’m not sure. I mean, let people make their own determination.” 

“I honestly have never looked at it,” he said. “As somebody said, he’s not. And I retweeted it. I have 14 million people between Twitter and Facebook and Instagram and I retweet things, and we start a dialogue and it’s very interesting.”

It is also very interesting to remember that Trump didn’t think there was any problem with Cruz’s eligibility last summer and admitted in a January debate that he only raised the issue because Cruz was gaining in the polls.

Is there any merit to Trump’s latest line of attack on Rubio?  Rachel Stockman of Law Newz looked into it and had this to say:

When I reached out to my usual Constitutional legal experts to ask about Rubio — even those that think Cruz’s eligibility is debatable —  most of them were too flabbergasted by the statement’s ridiculousness to give me a serious response.

Rick Hasen, a professor at the University of California-Irvine School of Law, was kind enough to provide a quote.

“The claim is meritless. I’m unaware of any serious scholar or court suggesting that someone born on U.S. soil is not a natural-born citizen if his parents were not citizens at the time,” Hasen told LawNewz.com. Hasen runs the popular electionlawblawg.com.

Rubio was rapidly gaining ground on Trump in the days before Saturday’s South Carolina primary to the point one poll had him within three percentage points. The Florida senator finished in second place, and spent Sunday declaring himself Trump’s strongest rival for the GOP nomination.

He says he is not fazed by Trump’s sudden line of attack. “This is a pattern,” Rubio said later on This Week. “This is a game he plays. He says something that’s edgy and outrageous and then the media flocks and covers that and then no one else can get any coverage on anything else.”

“And that worked when there were 15 people running for president. It’s not going to work anymore. I’m going to spend zero time on his interpretation of the Constitution with regards to eligibility.”