“Subject to the receipt of further information, I will be allowing, as President, the long blocked and classified JFK FILES to be opened,” Mr. Trump said on Twitter.

Subject to the receipt of further information, I will be allowing, as President, the long blocked and classified JFK FILES to be opened.

— Donald J. Trump (@realDonaldTrump) October 21, 2017

Mr. Trump has the power to block the release of the documents, and intelligence agencies have pressured him to do so for at least some of them. The agencies are concerned that information contained in some of the documents could damage national security interests.

In a statement to reporters, the White House left open the possibility that Mr. Trump might halt the release of some documents.

“The president believes that these documents should be made available in the interests of full transparency unless agencies provide a compelling and clear national security or law enforcement justification otherwise,” the statement said.

It is not known what revelations might be contained in the unreleased documents, though researchers and authors of books about Kennedy say they do not expect any bombshells that significantly alter the official narrative of the assassination — that Lee Harvey Oswald acted alone in Dallas — delivered in 1964 by the Warren Commission.

But the documents are likely to “help fuel a new generation of conspiracy theories,” according to Philip Shenon, a former New York Times reporter and the author of a book about the commission, and Larry J. Sabato, a University of Virginia professor and author of a book about Kennedy, who wrote a recent article about the documents in Politico.

They wrote that the documents relate to what they call a “mysterious chapter in the history of the assassination — a six-day trip that J.F.K. assassin Lee Harvey Oswald paid to Mexico City several weeks before the president’s murder, in which Oswald met with Cuban and Soviet spies and came under intensive surveillance by the C.I.A.’s Mexico City station. Previously released F.B.I. documents suggest that Oswald spoke openly in Mexico about his intention to kill Kennedy.”

With the Oct. 26 deadline to release the remaining documents fast approaching, Mr. Trump had been under increasing pressure from advocates of transparency not to hold back any of the documents from the public on the grounds of national security.

Senator Charles E. Grassley, Republican of Iowa, introduced a resolution in the Senate this month that urged Mr. Trump to make a “full public release of all remaining records,” saying that he should “reject any claims for the continued postponement of the full public release of those records.”

Conspiracy theorists have long clamored for what they hope will be evidence to prove that the government covered up the truth about the assassination. This week, Roger J. Stone, a friend of Mr. Trump’s, told Alex Jones, the radio host and conspiracy theorist, that Mr. Stone had directly urged the president to release all the documents.

“I had the opportunity to make the case directly to the president of the United States by phone as to why I believe it is essential that he release the balance of the currently redacted and classified J.F.K. assassination documents,” Mr. Stone said on Mr. Jones’s radio program.

Mr. Trump is no stranger to conspiracy theories, including those involving the Kennedy assassination. During the presidential campaign, he at one point alleged that the father of Senator Ted Cruz, a Republican primary rival from Texas, had been with Oswald shortly before Kennedy was killed.

“You know, his father was with Lee Harvey Oswald prior to Oswald’s being — you know, shot,” Mr. Trump told Fox News in an interview in May 2016, as he battled the Texas senator for the nomination. “I mean, the whole thing is ridiculous. What is this, right, prior to his being shot, and nobody brings it up. They don’t even talk about that. That was reported and nobody talks about it. But I think it’s horrible.”

He went on, “What was he doing with Lee Harvey Oswald shortly before the death, before the shooting? It’s horrible.”

Mr. Trump has at times dabbled in other conspiracy theories: He once seemed to consider the possibility that Justice Antonin Scalia had been murdered. The president has more than once spread the discredited urban legend about Muslims being shot with bullets dipped in pig’s blood. And for years, he was the most vocal purveyor of the falsehood that President Barack Obama was born outside the United States.

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http://www.nytimes.com/2017/10/21/us/politics/trump-jfk-assassination-classified.html