During an interview for "This Week," real estate mogul Donald Trump questioned whether Texas Sen. Ted Cruz would be eligible for the White House given his Canadian birth.

"If he was born in Canada, perhaps not." Trump told ABC's Jonathan Karl.

"I don't know the circumstances. I heard somebody told me he was born in Canada. That's really his thing," he said.

Trump also defended his previous accusation that President Obama may not actually have been born in the United States - a conspiracy theory that has been proven false - when asked about the issue by Karl.

"Well, I don't know, was there a birth certificate? You tell me. You know some people say that was not his birth certificate. So maybe it was; maybe it wasn't," Trump said.

ABC News

The interview took place in Ames, Iowa - where Trump spoke at an evangelical gathering on Saturday night. The billionaire businessman said he is considering a presidential run - although he said he won't make a final decision until after the 2014 midterm elections. He also said - if he did run - that he'd be willing to spend up to half a billion dollars.

When asked about his net worth, a subject of consistent speculation, Trump said he is probably worth over ten billion dollars ( Forbes pegged it recently at 3.2 billion ).

"I'd be willing to spend that kind of money. I'd spend whatever it took," he said, after Karl offered that modern presidential campaigns can cost 500 million dollars.

Trump, who said Hillary Clinton would be "very tough" to beat if she is the Democratic nominee for president in 2016, also weighed in on why Mitt Romney lost the presidential election last year.

"Mitt Romney was, in theory, I mean, should have been good but it didn't work. He didn't resonate," he said.

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