• President Donald Trump reportedly asked Deputy Attorney General Rod Rosenstein whether he was "on my team" during a meeting in December.
  • The interaction is the third known instance during which Trump asked a top law-enforcement official where their loyalties lie.
  • Rosenstein is increasingly emerging as a crucial witness in the Russia investigation, and experts said the reported interaction is an important new piece of evidence for special counsel Robert Mueller as he examines whether Trump sought to obstruct justice.

The special counsel, Robert Mueller, may have been handed another key piece of the puzzle as he investigates Russia's interference in the 2016 US election and whether President Donald Trump sought to obstruct justice.

CNN reported Wednesday that Trump asked Rod Rosenstein, the deputy attorney general, if he was "on my team" during a meeting at the White House in December.

Rosenstein reportedly replied, "Of course, we're all on your team, Mr. President."

Trump also asked Rosenstein about how the Russia investigation was coming along, which Rosenstein declined to comment on, according to the report. Their meeting came as Rosenstein was preparing to testify before the House Judiciary Committee.

Rosenstein reportedly went to the White House at the time to request Trump's help in pushing back against document requests from embattled House Intelligence Committee chairman Devin Nunes, who has been conducting his own investigation into alleged bias at the Department of Justice and FBI.

Instead, Trump was said to have focused on Rosenstein's upcoming House Judiciary Committee testimony, the report said.

The hearing, which took place on December 13 last year, was scheduled as part of the committee's normal oversight functions. But Republicans spent most of their time grilling Rosenstein about whether what they characterized as bias by some former agents who worked on Mueller's team had tainted the entire Russia investigation.

A consistent pattern

The interaction between Trump and Rosenstein marks the third known instance during which the president asked a top law-enforcement official where their loyalties lie.

The first occurred last year, shortly after Trump's inauguration. Former FBI director James Comey said in his prepared remarks for the Senate Intelligence Committee in June 2017 that Trump asked him for his loyalty during a private dinner months earlier, in January.

Comey said he declined to pledge his loyalty to Trump, adding that the interaction "concerned" him "greatly" because he believed Trump was "trying to create some sort of patronage relationship," in which Comey would keep his job as FBI director as long as he remained loyal to the president.

The next month, Trump asked Comey to let go of the FBI's investigation into former national security adviser Michael Flynn, who had resigned one day before. Three months later, after Comey refused to drop the Flynn probe, Trump fired him.

The White House first said Comey had been fired because of how he handled the investigation into former Secretary of State Hillary Clinton's use of a private email server, but Trump later told NBC's Lester Holt that "this Russia thing" had been a factor in his decision.

The second instance during which Trump questioned a top official's loyalty took place shortly after Comey's firing. The Washington Post reported last week that following Comey's ouster, Trump met with then-acting FBI director Andrew McCabe and asked him who he voted for during the 2016 presidential election. McCabe, who reportedly said he did not vote in the election that year, found the question to be "disturbing," one official told The Post.

Though the White House tapped McCabe to be acting FBI director, Trump quickly soured on him as the Russia probe picked up steam last year. McCabe was finally forced out of the bureau earlier this week following months of sustained attacks on his credibility from Trump and his loyalists.

McCabe is one of three officials Comey apprised of his conversations with Trump, which are now being scrutinized by Mueller and congressional investigators. The other two, former FBI general counsel James Baker and Comey's former chief of staff James Rybicki, were replaced or reassigned within the bureau.

FBI director Christopher Wray indicated that McCabe's removal was the result of a Justice Department investigation into his handling of the Clinton email investigation. But the deputy director's defenders questioned the timing of the move, given that it came amid Trump's criticisms, as well as Attorney General Jeff Sessions' reported request that Wray replace McCabe at the bureau.

Comey's firing and Trump's subsequent actions make up the basis of Mueller's inquiry into whether he sought to obstruct justice in the Russia investigation. Obstruction of justice is broadlydefined: it involves any conduct in which a person willfully interferes with the administration of justice.

Rosenstein's reported interaction with the president indicates that he is becoming an increasingly crucial witness for Mueller and congressional investigators.

The December conversation represents the "same pattern of behavior that Trump engaged in with Comey," former federal prosecutor Renato Mariotti wrote on Twitter. "At this point, there can be little question that Rosenstein will be a witness for Mueller. It's hard to see how he can continue to oversee the Mueller investigation."

The possibility of Rosenstein's recusal is not new. The deputy attorney general attracted scrutiny last year when Trump said he had authored a memo that played a pivotal role in Comey's firing. Questions were raised at the time about whether Rosenstein should recuse himself from the Russia probe, but Cramer said Wednesday that the latest revelations indicated that they may soon reach fever pitch.

Cornell Law School vice dean and criminal law expert Jens David Ohlin agreed, saying Rosenstein's failure to recuse himself has long been a source of speculation in the legal community, and that recent developments would only accelerate that speculation.

He added that there are several theories that could account for Rosenstein's apparent lack of willingness to recuse himself. "Bottom line: this is a mystery that probably won't get resolved until the Mueller investigation is over," he said.

Mariotti said Rosenstein is now a potentially critical witness for two key reasons:

If Rosenstein recuses himself, the associate attorney general, Rachel Brand, would be next in line to oversee Mueller's investigation. Trump could seek to appoint a new deputy attorney general, Cramer said, but the confirmation would likely be difficult under current circumstances.