But once the two countries were engaged in an armed conflict, Mr. Goldsmith said, the United States could lawfully strike nuclear installations with a military dimension. Still, he said, if that is the only sort of attack the Trump administration has in mind, that would mean any invocation of purported Qaeda links to justify the conflict would seem “pretextual.”

Why else would interpreting the war law to cover Iran be disputed?

Nobody can plausibly contend that when Congress enacted the law in 2001, lawmakers understood themselves to be authorizing a war against Iran in 2019. The 9/11 Commission report also said it found no evidence that Iran was aware of Al Qaeda’s planning for those attacks. And Iran lost that 2011 lawsuit by default because it did not bother to send lawyers to court to contest the plaintiffs’ claims.

Moreover, Iran’s government is run by Shiite Muslims, while Al Qaeda and its affiliates are Sunni Muslims who consider Shiites to be apostates. There is no public evidence that Iranian forces and Al Qaeda carried out joint operations, and Qaeda-linked terrorists have attacked Shiite shrines and other targets, including inside Iran.

Ali Soufan, a former F.B.I. agent who investigated and has written extensively about Al Qaeda, said that Iran was a menacing actor whose activities do pose a threat to American national security interests and to regional stability in various ways, but a relationship with Al Qaeda is not one of them.

Citing letters that showed hostility toward Iran that were seized in the raid on Osama bin Laden’s compound, Mr. Soufan compared recent discussion of Iran-Qaeda links to misleading hype about Iraq-Qaeda links before the 2003 invasion. One example: stressing that Bin Laden’s son Hamza lived for years in Iran without mentioning the context: He was a prisoner.

“I think what is happening now is we are witnessing cherry-picked intelligence in order to manipulate a particular narrative,” Mr. Soufan said.