(Reuters) - In 1997, Neil Eggleston represented Bill Clinton’s administration at the District of Columbia U.S. Court of Appeals in a fight over documents from the White House’s internal investigation of onetime cabinet member Mike Espy. Espy was under scrutiny from an independent counsel, Donald Smaltz, for allegedly accepting gifts from organizations with business before his department. Smaltz, who was conducting a grand jury investigation, wanted to see what Clinton’s advisers had turned up in their own inquiry. Eggleston argued the subpoenaed documents were shielded by executive privilege.

The D.C. Circuit agreed that a president’s communications with his advisers are protected by executive privilege. But the court also held that Smaltz was entitled to see certain subpoenaed documents if he could show both that he needed the information they contained to complete his investigation and that he could not obtain the information from any other source.

Espy was ultimately acquitted on charges of illegally accepting gratuities but his 20-year-old case is suddenly back in the news because of President Trump and special counsel Robert Mueller. The president's lawyers are relying on the D.C. Circuit’s Espy precedent in the special counsel’s investigation into alleged Russian meddling in the 2016 election. In a letter delivered to Mueller in January and published Sunday by The New York Times, Trump attorney John Dowd said Mueller was not entitled even to an interview with the president because the special counsel could not pass the Espy test for need and unavailability.

The president, Dowd said, has already turned over thousands of documents and has allowed his advisors to appear for interviews with Mueller’s team, providing enough information to answer all of the special counsel’s questions about potential collusion and obstruction of justice. “In light of these voluntary offerings, your office clearly lacks the requisite need to personally interview the president,” the letter said. Dowd no longer represents President Trump but his replacement, Rudy Giuliani, said Sunday that the president’s legal strategy is unchanged. If the special counsel attempts to subpoena the president’s testimony, it’s a good bet that the president’s lawyers will cite Espy in an attempt to squelch the subpoena.

But according to Eggleston, the lawyer who litigated the case for the Clinton White House, Trump’s legal team is “misreading” Espy precedent. In the Espy case, he said, independent counsel Smaltz was after documents showing what the president’s advisers thought about allegations against the onetime cabinet officer. As the D.C. Circuit opinion made clear, President Clinton had not personally seen some of the subpoenaed material. That’s a distinct contrast from Mueller’s request to interview President Trump, Eggleston said.

“It’s completely different,” he told me. “In Espy, the information the independent counsel was attempting to get was available through other witnesses. Here, the knowledge and state of mind of the president is completely relevant and the special counsel can only get that information from the president himself.”

In other words, according to Eggleston, the Trump team’s faith in Espy is misplaced because no other witness or documents can prove what was in the president’s head – and that’s information Mueller needs to complete his investigation. (As you probably recall, and as the D.C. Circuit discussed in its Espy opinion, the U.S. Supreme Court imposed a similar need and unavailability test in 1974’s U.S. v. Nixon, when the justices required President Nixon to turn over subpoenaed tape recordings. The Nixon case involved a subpoena in the criminal trial of the president’s confederates; Espy involved a grand jury subpoena.)

Trump’s lawyers argued in their letter to Mueller that the president has already provided documents and testimony that allow the special counsel to understand his knowledge and state of mind “in a significant and exhausting manner.” I emailed a request for comment on Eggleston’s contrary view to a Giuliani representative. She said he was traveling and unavailable for comment. Espy independent counsel Donald Smaltz told me he hadn’t yet read the Trump lawyers’ letter and could not immediately comment.

Law professor Stephen Vladeck of the University of Texas said the Trump team had picked the right precedent in Espy, but seemed to be overreading the D.C. Circuit’s holding. “It’s true that Espy says grand jury subpoenas have to meet a higher standard,” Vladeck said. “But Mueller could probably satisfy Espy if the president is being called to testify about things he said or thought.”

Russia has denied U.S. intelligence agencies’ assessment that Moscow sought to interfere with the 2016 U.S. presidential election to boost Donald Trump’s prospects. Trump has also said there was no collusion by his campaign.

President Trump’s lawyers cited a 1999 paper on executive privilege precedent in Espy and other Clinton-era cases for the proposition that case law requires independent investigators to provide “detailed documentation of efforts to obtain the needed information from other sources.” The paper, which appeared in the Akron Law Review, was written by James Popson, at the time a law student at the University of Akron and now a partner at Cleveland’s Sutter O’Connell.

Popson told me he considered it “an honor and kind of humbling” to have been mentioned in the president’s letter. He said Trump’s lawyers had fairly and accurately represented his paper, noting that the point on which they cited him was “relatively elementary.”

So did Popson, whose practice includes defending police officers in civil rights cases, agree with President Trump’s assessment of Espy precedent? “It’s a murky area of the law,” he said. “I have no opinion as to who’s right or wrong.”