WASHINGTON — As the special counsel’s investigators pursued the question of whether President Trump tried to impede their work, they uncovered compelling evidence — a voice mail recording and statements from a trusted witness — that might have led to him.
A lawyer for Mr. Trump, John M. Dowd, reached out to a lawyer for a key witness who had just decided to cooperate with the government, Michael T. Flynn. Mr. Dowd fished in his message for a heads-up if Mr. Flynn was telling investigators negative information about Mr. Trump — while also appearing to say that if Mr. Flynn was just cutting a deal without also flipping on the president, then he should know Mr. Trump still liked him.
But the president’s role, if any, remains a mystery. Mr. Dowd never said whether Mr. Trump directed him to make the overture. And investigators for the special counsel, Robert S. Mueller III, declined to question Mr. Dowd about his message, citing “attorney-client-privilege issues.”
The release of the recording last week served as a reminder that despite the considerable evidence laid out in the 448-page Mueller report, some tantalizing questions about the president’s conduct went unanswered because investigators encountered obstacles or backed off on pursuing leads.
Mr. Dowd could have told investigators whether Mr. Trump knew about his message and had directed him to convey it, and whether any such conversation included dangling a veiled suggestion of a potential pardon at Mr. Flynn. The question is whether it amounted to witness tampering.
Legal experts were divided on whether Mr. Mueller’s team should have sought to question Mr. Dowd. The investigators compiled substantial evidence that Mr. Trump tried to obstruct justice even without Mr. Dowd’s testimony, and an attempt to interview him could have set off a lengthy court battle with an uncertain outcome.
“Given all that Mueller’s team had on their plate, it doesn’t strike me as unreasonable for them to have said, ‘This is not what we want to spend our time on,’” said David A. Sklansky, a Stanford law professor and a former criminal prosecutor.
But questioning Mr. Dowd about whether Mr. Trump wanted him to dangle pardons or other favorable treatment to witnesses might have been a worthy investigative pursuit because it would have cut to the heart of whether the president abused his power.
Joyce Vance, a professor at the University of Alabama School of Law and a former United States attorney, said she would have wanted to use all tools available to learn whether Mr. Trump told Mr. Dowd to make the call.
She noted that courts have recognized an exception to attorney-client privilege that allows investigators to compel people to testify to a grand jury about such conversations if they are involved in the commission of a crime.
“Lawyers can’t engage in criminal conduct disguised as legal representation,” she said.
Ms. Vance said that seeking to interview Mr. Dowd “seems so obvious” that there may be details that have yet to become public that shed light on the Mueller team’s decision.
Mr. Dowd did not respond to a message seeking comment. He has reacted angrily to the report’s portrayal of his messages, calling it “a baseless, political document designed to smear and damage the reputation of counsel and innocent people,” and stressing that the special counsel never even asked him about the voice mail message.
Other presidents have faced immense scrutiny for the same issue. In 1974, one of the articles of impeachment against Richard M. Nixon said he had sought to signal to defendants in the Watergate investigation that they would be treated favorably “in return for their silence or false testimony.”
A transcript of Mr. Dowd’s message for Mr. Flynn’s lawyer at the time, Robert K. Kelner, was included in the Mueller report, which was made public in April. But the audio, released after prosecutors said they no longer needed to keep it under seal, added new texture to the episode.
The report laid out a string of communications between Mr. Dowd and Mr. Flynn’s lawyers around the decision by their client, the president’s first national security adviser, to cooperate with Mr. Mueller’s prosecutors. That move effectively ended the joint defense agreement that the lawyers had operated under for months and that had allowed them to share information about the investigation.
After Mr. Kelner told Mr. Dowd that they could no longer work together, Mr. Dowd left the voice mail message that Mr. Mueller’s team later obtained, saying that if Mr. Flynn had information that could incriminate the president, he should share it because that might create a “national security issue.”
“We need some kind of heads-up” if Mr. Flynn was planning to give investigators negative information about Mr. Trump, Mr. Dowd said.
Mr. Dowd then added that “if it’s the former” — an apparent reference to an earlier part of his message, when he raised the possibility that Mr. Flynn had struck a plea deal to end his own legal troubles — then Mr. Flynn should “remember what we’ve always said about the president and his feeling toward Flynn, and that still remains.”
It is unclear what Mr. Dowd meant by a “national security issue” — or why Mr. Trump’s personal lawyer, as opposed to a government lawyer, would have any role in thinking about it.
At the time, Mr. Trump’s lawyers were concerned about Mr. Mueller’s investigation into whether he was tied to Russia’s election interference. Mr. Flynn was also under investigation for his ties to Russia. And as Mr. Trump’s national security adviser for less than a month, he had access to many of the country’s most heavily guarded secrets.
Mr. Kelner returned the call the next day — on Thanksgiving — according to the report, again saying that he and his client could no longer share information.
Mr. Dowd reacted indignantly. “He interpreted what they said to him as a reflection of Flynn’s hostility toward the president” and planned to tell Mr. Trump so, the report said, citing an F.B.I. interview of Mr. Kelner.
Mr. Dowd’s call, investigators wrote, played out against the backdrop of a pattern in which Mr. Trump had “sent private and public messages to Flynn encouraging him to stay strong and conveying that the president still cared about him” before he began to cooperate with investigators.
Yet Mr. Mueller’s investigation of that episode essentially stopped there. In addition to citing in a footnote the attorney-client-privilege issues that kept them from questioning Mr. Dowd, investigators also agreed after months of negotiations to accept written answers from Mr. Trump, who refused to address obstruction issues, rather than subpoena him for an interview.
Around the time Mr. Flynn decided to cooperate, Mr. Dowd told others that he told Mr. Kelner that the president was prepared to pardon his client because he had long believed that the case against Mr. Flynn was weak, a person familiar with the matter has said. That detail, reported in The New York Times in March 2018, was not in the Mueller report.
One way of interpreting the episode is that Mr. Dowd was telling Mr. Flynn not to provide the government with damaging information about Mr. Trump even if he cooperated in other ways, and suggesting that Mr. Trump might reward his loyalty with a pardon.
But the message was ambiguous. Mr. Dowd never mentioned pardons specifically. The Mueller report said only that the call and other events “could have had the potential to affect Flynn’s decision to cooperate, as well as the extent of that cooperation.”
By contrast, the report is far more explicit about Mr. Trump’s conduct toward his former campaign chairman, Paul Manafort. Evidence shows that Mr. Trump sought to discourage Mr. Manafort from cooperating with the government and intended to influence a jury weighing whether to convict him, according to the report.
Analyzing the episode begins with trying to make sense of what Mr. Dowd was saying in his circular, halting way, legal experts said.
His message might be interpreted “as a thinly veiled offer of a pardon conditioned on Flynn keeping his mouth shut,” Mr. Sklansky said.
If so, he said, that would amount to obstruction of justice, and any conversations between the president and Mr. Dowd about sending such a message to Mr. Flynn would no longer be protected by attorney-client privilege because they would be considered part of a crime. In that case, a judge might have ordered Mr. Dowd to comply with a subpoena to disclose the discussions.
However, Mr. Sklansky stressed, all of that depends on two things that remain unclear: whether that is the correct interpretation of Mr. Dowd’s remarks and whether Mr. Trump in fact told him to send that message with corrupt intent. And because Mr. Dowd would certainly have invoked attorney-client privilege to avoid voluntarily answering questions about those interactions, he said, it would mean a lengthy subpoena fight in court for his testimony.
It was probably not worth it for Mr. Mueller’s investigators to take on that challenge — especially if all they had to make the case to a judge were their suspicions about a difficult-to-parse statement, said Samuel W. Buell, a former federal prosecutor who now teaches criminal law at Duke University.
“It’s a little bit of a Catch-22 because the privilege is so carefully protected by the courts that the exceptions only kick in when you can show they apply,” Mr. Buell said. “How can you show they apply before you have that information? You have to have a circumstantial case already that someone and their lawyer were engaging in obstruction before you can get to the conversations between them.”
Mr. Buell also noted that it was common for defense lawyers to fish around for information that might be helpful to their client, and while Mr. Dowd’s comments may have walked “somewhat dangerously close to the line,” Mr. Buell’s assessment was that “it strikes me as veiled enough that it’s nothing a prosecutor could base a witness-tampering charge on.”