By Adam Liptak

Seth Barrett Tillman is a lecturer in the law department of Maynooth University in Ireland. He is, he said in a recent court filing, a “lonely scholar with unusual ideas, who is unaffiliated with the popular, the organized and the wealthy.d

One of his unusual ideas is that President Trump cannot be sued for violating the Constitution’s foreign emoluments clause, which prohibits federal officials from taking payments from foreign governments.

Several lawsuits have accused Mr. Trump of violating the clause by doing business with entities controlled by foreign governments. If Mr. Tillman is right, those lawsuits should be dismissed.

In June, Mr. Tillman filed a friend-of-the-court brief saying that some framers of the Constitution did not think the emoluments clause applied to the president. One of his key pieces of evidence was a document signed by Alexander Hamilton.

The reaction was swift and brutal. Legal historians and a lawyer for members of Congress suing Mr. Trump said Mr. Tillman had misunderstood, misrepresented or suppressed crucial contrary evidence.

Jed Shugerman, a law professor at Fordham, wrote a blog post urging Mr. Tillman to issue a correction. “One might expect,” Professor Shugerman wrote, “that when a brief before a court contains significant factual errors or misleading interpretations of evidence, the authors of that brief will offer to correct their briefs or retract the sections if they are no longer supported by the evidence.”

In another blog post, Brianne J. Gorod, a lawyer with the Constitutional Accountability Center, which represents lawmakers suing Mr. Trump, said Mr. Tillman’s account was “not accurate, not even remotely so.”

Five legal historians, including Professor Shugerman, filed their own friend-of-the-court brief. They said Mr. Tillman’s had “incorrectly described” the evidence in a footnote in his brief.

Mr. Tillman took none of this lightly. In a sworn statement last week, he repeated his original position. “I stand entirely behind the above footnote: behind every sentence, every phrase, every word and every syllable,” he wrote. “I made no mistake, intentional or inadvertent. I retract nothing, and I do not intend to retract anything.”

Mr. Tillman, who is represented by Josh Blackman, an energetic law professor and litigator, rounded up declarations from experts in founding-era documents and on Hamilton. They agreed that the document said to contradict Mr. Tillman’s account was not signed by Hamilton and was prepared after his death.

I asked Mr. Tillman’s critics for their reactions. Professor Shugerman responded with “a public and personal apology.”

“I am satisfied that Tillman and Blackman have provided support for their perspective on these documents,” he wrote on his blog.

“I was wrong to suggest that Tillman misused sources, and I was wrong to question his credibility,” Professor Shugerman wrote. “Tillman is a diligent, creative, intelligent and learned scholar who deserved more respect than the way I handled these exchanges. I’m sincerely sorry for any trouble or hardship I caused for Mr. Tillman and his family.”

Professor Shugerman’s fellow historians — John Mikhail, Jack Rakove, Gautham Rao and Simon Stern — said they were still studying the matter. Ms. Gorod did not offer a direct response.

“While there is a fascinating academic discussion to be had about the provenance of these particular documents, and that specific discussion will surely continue, it’s ultimately immaterial to what’s going on in the courts because at the end of the day, it is clear that the foreign emoluments clause applies to the president,” she said in statement. “Even the Department of Justice agrees.”

She is right that the cases are very unlikely to turn on Mr. Tillman’s arguments. All of the parties, including Mr. Trump’s lawyers, agree that the foreign emoluments clause applies to the president.

The Justice Department instead argued that Mr. Trump had not violated the clause because he had taken no money in exchange for his official actions.

Mr. Tillman said the clause does not apply to the president in the first place, pointing to a 1793 document submitted by Hamilton, who was the secretary of the Treasury. The Senate had asked him to list “every person holding any civil office or employment under the United States.” That language tracks but is a little broader than what is in the emoluments clause, which was not the subject of the request.

In Hamilton’s response, which the editors of his papers say he signed, he did not list the president or any other elected official.

That is some evidence, though more than a little indirect, about what one of the framers of the Constitution thought about how broadly the emoluments clause swept.

In his brief, Mr. Tillman noted but discounted a contrary piece of evidence. “An entirely different document (but bearing a similar name),” he wrote, did include the president. It was “undated,” “not signed by Hamilton” and “was drafted by an unknown Senate functionary.”

Mr. Tillman’s critics said that second document was the crucial one, adding that it bore both a date and Hamilton’s signature.

In court papers Mr. Tillman sought to file last week, he argued that the second document was “a scrivener’s copy — the antebellum equivalent of a photocopy — which was not signed by Hamilton.” Indeed, Mr. Tillman said, internal evidence in the second document indicated that it “was drafted long after Hamilton’s death in 1804.”

Judge George B. Daniels of the Federal District Court in Manhattan promptly rejected Mr. Tillman’s request to file more papers, which, after all, concerned an issue that is not disputed between the parties.

Mr. Tillman’s plea, though, was probably addressed to an audience wider than a single judge. It has yielded a gracious apology, and it has demonstrated a couple of things.

The lawsuits are bitterly contested because they are important. And, whatever the value of using indirect evidence to interpret the Constitution, the demands of historical research and vigorous legal advocacy can tug in different directions.