President Donald Trump has reportedly ignored his lawyers' advice and had at least two conversations with witnesses in the Russia investigation to ask them about issues they discussed with the special counsel Robert Mueller.

Those witnesses, according to The New York Times, were the White House counsel, Don McGahn, and Trump's former chief of staff, Reince Priebus. Both men were present for critical events that have contributed to Mueller's obstruction-of-justice case against Trump.

Mueller is said to have become aware of Trump's conversations after witnesses and their lawyers informed him of them, reportedly because they found the interactions to be problematic.

Asking witnesses about matters related to Mueller's inquiry would add yet another piece of evidence to the special counsel's growing arsenal in the obstruction case.

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President Donald Trump has had at least two conversations in recent months with key witnesses in the Russia investigation, during which he asked them about matters they discussed with the special counsel Robert Mueller, The New York Times reported Wednesday.

Mueller is aware of the conversations, the report said, which Trump apparently had with witnesses against his lawyers' advice.

In one instance, Trump reportedly told an adviser that the White House counsel Don McGahn should issue a statement denying a Times article in January that said Trump asked McGahn to order Mueller's firing. McGahn did not issue any such statement, and, according to The Times, McGahn reminded Trump that the president had, in fact, asked him to order Mueller's dismissal.

In another, Trump asked his former chief of staff, Reince Priebus, how Priebus' interview with Mueller's team had gone and whether the prosecutors had been "nice," the report said.

The Times said Mueller learned of the conversations when the witnesses and their lawyers informed him of them because they viewed the interactions as problematic.

The conversations will most likely contribute to the obstruction-of-justice case Mueller has been building against Trump since Trump fired FBI Director James Comey in May.

The White House initially said Comey was fired because of the way he handled the FBI's investigation into Hillary Clinton's use of a private email server while she was secretary of state. But Trump later said on national television that "this Russia thing" was a factor in his decision. Comey publicly confirmed the existence of the FBI's Russia investigation two months before he was fired.

To prove that Trump tried to obstruct justice, prosecutors need to establish the president's mindset and show that he acted with "corrupt intent."

"Telling McGahn to lie to the public about his order to fire Mueller is not a crime, but it shows that Trump was concerned about the truth coming out and/or that he had a guilty conscience," the former federal prosecutor Renato Mariotti wrote on Twitter.

"That episode alone is not witness tampering unless Mueller could prove that it was done to influence McGahn's testimony or statement to Mueller," Mariotti added. "It doesn't appear to have been successful, in any event."

Indeed, The Times reported in January that Trump had asked McGahn to order Mueller's firing but that McGahn instead threatened to resign.

McGahn is a critical witness in the Russia investigation. In addition to being privy to Trump's day-to-day musings about what the president characterizes as a "witch hunt" and a "hoax," McGahn also reportedly urged Trump not to send the Department of Justice a draft letter, the weekend before he fired Comey, outlining the reasons he wanted to dismiss the FBI director.

"We don't know exactly what McGahn said, but the mere fact that he put a stop to that letter is another piece of evidence that Mueller could use to say, 'Donald Trump was warned by the White House counsel that this was a problematic step and decided to do it anyway,'" Mariotti told Business Insider last year.

"If he said anything along the lines of, 'There's potential criminal liability if you shut down this investigation,' that would be extraordinarily powerful evidence against Trump."

Trump also reportedly asked McGahn last April to help persuade Comey to publicly clear him in the Russia investigation.

McGahn subsequently called then-Deputy Acting Attorney General Dana Boente and asked him to persuade Comey to exonerate Trump, but the request fell on deaf ears, according to The Washington Post. Boente is now the FBI general counsel.

Mariotti wrote on Wednesday that Trump's question to Priebus about whether investigators had been "nice" to him "could suggest that he's concerned about being interviewed in the investigation. Mueller could argue that this suggests Trump has something to hide, which could explain why he fired Comey."

Trump's lawyers have worked overtime in recent months to sidestep a face-to-face interview between the president, who has been known to exaggerate the truth and make misleading statements in the past, and the special counsel.

At first, Trump's personal defense lawyers suggested providing written answers to a predetermined set of questions or submitting a signed affidavit saying Trump did nothing wrong.

As things progressed, however, Trump's defense team began structuring a legal argument around the claim that Mueller had not met the required standard to merit an interview with Trump and that a potential interview could set a dangerous legal precedent.

Experts threw cold water on both arguments, calling them "weak" and "dubious," and added that they were unlikely to succeed.

Based on public reporting and conversations with people close to the matter, Mueller's obstruction case appears closer to concluding than his investigation into whether members of Trump's campaign colluded with Moscow to tilt the 2016 US election in his favor.

In addition to Comey's firing, the special counsel is also looking into Trump's role in crafting an initially misleading statement his son Donald Trump Jr. released last year in response to reports that he met with two Russian lobbyists offering dirt on Clinton in June 2016, at the height of the presidential campaign.