"It was a retweet -- not so much with Marco. I'm not really that familiar with Marco's circumstance," Trump said on ABC.
Click through some of Donald Trump's most controversial Tweets:
Craziest Donald Trump Tweets
Trump says he's 'not sure' if his opponents can legally be president
I told you @TIME Magazine would never pick me as person of the year despite being the big favorite They picked person who is ruining Germany
I would like to wish everyone, including all haters and losers (of which, sadly, there are many) a truly happy and enjoyable Memorial Day!
Just made the point at #NCGOPcon that "we have to protect our border & I think everyone here knows, nobody can build a wall like Trump!"
My twitter has become so powerful that I can actually make my enemies tell the truth.
China's Communist Party has now publicly praised Obama's reelection. They have never had it so good. Will own America soon.
While Jon Stewart is a joke, not very bright and totally overrated, some losers and haters will miss him & his dumb clown humor. Too bad!
Why is Obama playing basketball today? That is why our country is in trouble!
An 'extremely credible source' has called my office and told me that @BarackObama's birth certificate is a fraud.
Remember, I said Derek don't sell your Trump World Tower apartment...its been lucky for you. The day after he sold it, he broke his foot.
I never fall for scams. I am the only person who immediately walked out of my ‘Ali G’ interview
.@cher--I don’t wear a “rug”—it’s mine. And I promise not to talk about your massive plastic surgeries that didn’t work.
The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive.
.@katyperry is no bargain but I don't like John Mayer--he dates and tells--be careful Katy (just watch!).
.@BetteMidler talks about my hair but I'm not allowed to talk about her ugly face or body --- so I won't. Is this a double standard?
It's Thursday. How much money did Barack Obama waste today on crony green energy projects?
Truly weird Senator Rand Paul of Kentucky reminds me of a spoiled brat without a properly functioning brain. He was terrible at DEBATE!
Hey @realDonaldTrump - In case you're looking for that tweet you deleted .. I got it right here. http://t.co/a6F98q5xGU
This very expensive GLOBAL WARMING bullshit has got to stop. Our planet is freezing, record low temps,and our GW scientists are stuck in ice
Everyone knows I am right that Robert Pattinson should dump Kristen Stewart. In a couple of years, he will thank me. Be smart, Robert.
26,000 unreported sexual assults in the military-only 238 convictions. What did these geniuses expect when they put men & women together?
Sorry losers and haters, but my I.Q. is one of the highest -and you all know it! Please don't feel so stupid or insecure,it's not your fault
How amazing, the State Health Director who verified copies of Obama’s “birth certificate” died in plane crash today. All others lived
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"But then why retweet it?" said George Stephanopoulos. "Because I'm not sure. I mean, let people make their own determination," Trump said.
Rubio was born in Miami to immigrant parents and Cruz in Canada to an American mother. Candidates don't actually have to prove eligibility unless they're challenged through a lawsuit.
Both Republican candidates have faced several of these cases, but all, so far, have been dismissed.
The legal case revolves around the requirement the president be a "natural born citizen," a phrase which isn't defined in the Constitution.
Both candidates have argued against a strict reading of the phrase, with Rubio saying it "would jeopardize centuries of precedent and deem at least six former presidents ineligible for office."
"The law under the Constitution, and federal law, has been clear from the very first days of the Republic. The child of a U.S. citizen born abroad is a natural born citizen," Cruz said at a town hall meeting.
Trump's eligibility questions go beyond the Republican race. In January, he told CNN someday he'll write a book on his theory regarding President Obama's eligibility.