De facto Republican presidential nominee Donald Trump doubled down on a wild conspiracy theory linking Sen. Ted Cruz's father to the assassination of President John F. Kennedy and defended the tabloid paper that made the claim.

"All I was doing was referring to a picture that was reported in a magazine," Trump said on ABC's "Good Morning America." "I think they didn't deny it. I don't think anybody denied it. No, I don't know what it was exactly, but it was a major story in a major publication, and it was picked up by many other publications."

Trump was widely criticized Tuesday for claiming that Cruz's father, Rafael Cruz, was spotted with Lee Harvey Oswald around the time of Kennedy's assassination. The business mogul seems to have been referring to a National Enquirer story from last month alleging that the elder Cruz appeared in a 1963 photo with Oswald, a claim the now-defunct Cruz campaign has called "garbage."

After ABC News anchor George Stephanopoulos questioned the tabloid's credibility -- it is perhaps best known for its alien sightings -- Trump defended the Enquirer's coverage of the O.J. Simpson murder trial and John Edwards's sex scandal in 2008.

"You can't knock the National Enquirer," Trump said.

"It's brought many, many things to light, not all of them pleasant. The fact is that [the supposed Cruz-Oswald photo] was a cover story on the National Enquirer. It was picked up by many other people and magazines and periodicals and newspapers, and all I did was refer to it. I'm just referring to an article that appeared. It has nothing to do with me."

Trump also accused Rafael Cruz of saying "nasty things" about him during the campaign.

Ted Cruz dropped out of the presidential race Tuesday night after Trump's runaway victory in the Indiana primary. Trump is now considered the presumptive Republican nominee, with only Ohio Gov. John Kasich -- his long-shot GOP rival -- left in the running.

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