Americans like transparency in their government, and so on December 15, the vast majority want President Biden to release all files related to President Kennedy’s 1963 assassination as mandated by law. But those hoping to find proof of a conspiracy are doomed to disappointment whether the president complies or not.

According to a poll conducted by Bendixen & Amandi International last month, 71 percent of registered voters want Mr. Biden to implement the President John F. Kennedy Assassination Records Collection Act, which was passed in 1992 without a single dissenting vote — meaning Mr. Biden himself voted for it when he was a senator.

Since the 2017 deadline set by the 102nd Congress, the National Archives has released hundreds of thousands of pages. But President Trump also ordered some documents withheld at the behest of the FBI and CIA, who said they’d harm the national interest.

Last year, Mr. Biden again kicked the can down the road, citing the Covid pandemic and writing in a statement, “Temporary continued postponement is necessary to protect against identifiable harm to the military defense, intelligence operations, law enforcement, or the conduct of foreign relations that is of such gravity that it outweighs the public interest in immediate disclosure.”

The Mary Ferrell Foundation sued Mr. Biden and the Archives in October demanding the release, and I asked investigative journalist and attorney Gerald Posner — whom I interviewed about Pulitzer Prize finalist “Case Closed: Lee Harvey Oswald and the Assassination of JFK” — what they think the government is withholding.

“In reality,” he wrote me via email, those seeking the files “are looking for something that I am confident does not exist, what they call Operation Oswald.” This is what his colleague, Jefferson Morley of JFK Facts, believes are “smoking-gun proof of a CIA operation involving Lee Harvey Oswald.”

“The problem,” Mr. Posner writes, “is that Morley has not seen the documents. No one has. It’s guesswork by anyone to claim they know what those files might reveal. In fact, they are not even part of the President John F. Kennedy Assassination Records Collection at the National Archives.”

Mr. Posner has provided exhaustive documentation that Oswald acted alone. For example, with technology unavailable to the Warren Commission, “We now know exactly how that ‘magic’ bullet happened,” he told me. “Ballistics experts can recreate it all day long.”

However, he wrote in a Substack post, “What is long overdue in the JFK assassination is full disclosure of relevant sealed government files. I urge the CIA to put the files identified by Morley into the Collection at the National Archives and process them as quickly as possible.”

The thing about conspiracy theories is that the absence of proof doesn’t convince their adherents. Consider the charges that President John Quincy Adams and Speaker of the House Henry Clay engaged in a “corrupt bargain”  to deny President Jackson the White House in 1824.

When Clay and Adams met, the president recorded their meeting in his diary with uncharacteristic brevity, writing in Latin “Incedo super ignes,” meaning “I walk over fire.” Based on Adams appointing Clay as secretary of state, this cryptic remark has been taken by generations as a confession of shenanigans.

This is also the case with Kennedy. “If the documents Morley seeks are made public and do not show what he says they do,” Mr. Posner says, “his fallback position will be that the definitive records were destroyed.”

Mr. Posner lays out the definitive case that Oswald acted alone in “Case Closed,” but encourages transparency. “As President Trump has started,” he said in our interview, “President Biden now has the ability to release as many files as possible.

“But it will not settle the debate for those who believe in a conspiracy. If you release every last document and it doesn’t provide a smoking gun about the conspiracy, they will say, ‘Oh, see, I knew it! They destroyed the evidence.’”

Full disclosure befits a republic, but no matter what Mr. Biden does on December 15, don’t expect it to be enough to convince those who cling to their belief in a plot to assassinate the 35th president. This myth, unlike people, is just too hard to kill.