Former White House chief of staff Reince Priebus. Associated Press/Alex Brandon

President Donald Trump's former chief of staff and current White House counsel have hired a lawyer following reports that special counsel Robert Mueller wants to interview them as part of his investigation into Russian interference in the 2016 election.

Reince Priebus, Trump's former chief of staff, and Don McGahn, the White House counsel, have hired William Burck, a prominent white-collar criminal defense attorney from Quinn Emanuel Urquhart & Sullivan, Law360 reported this weekend.

On Friday, it emerged that Mueller was seeking to question Priebus and McGahn as his team examines whether the Trump campaign colluded with Moscow to tilt the 2016 election in Trump's favor. In addition to the two men, Mueller also reportedly wants to speak to Hope Hicks, the interim communications director; Sean Spicer, the former press secretary; James Burnham, McGahn's deputy; and Josh Raffel, a top aide who works with Jared Kushner, Trump's son-in-law and senior adviser.

Each of the aides, The Washington Post reported, was witness to critical discussions that have drawn Mueller's scrutiny. Those events include Trump's bombshell decision to fire FBI Director James Comey in May, the administration's inaction after it was informed that its national security adviser Michael Flynn could be vulnerable to Russian blackmail, and Trump's role in crafting Donald Trump Jr.'s initially misleading statement about a meeting he took with a Kremlin-connected lawyer last June.

A former federal prosecutor named Renato Mariotti noted on Sunday that Priebus and McGahn's decision to hire the same lawyer could indicate that the two would mount a joint defense in Mueller's investigation. It may also suggest that Burck believes the two men will not be at odds with each other in the investigation and that they will be witnesses rather than defendants.

Priebus was privy to many significant discussions when he served as chief of staff, and he'll most likely be questioned about what he knows regarding Donald Trump Jr.'s meeting at Trump Tower last June with a Kremlin-connected lawyer, per Law360. Kushner, whom Raffel works for, was also present at the meeting, as was Trump’s campaign chairman, Paul Manafort.

White House counsel Don McGahn. Drew Angerer/Getty Images

McGahn was involved in several important discussions involving Flynn, who was ultimately ousted as national security adviser, and Comey.

McGahn first drew focus after Sally Yates, the former deputy attorney general, told the Senate Judiciary Committee in May that she had warned the White House about Flynn's conversations with Russia's ambassador to the US, Sergey Kislyak, that took place during the transition period. Flynn did not disclose his contacts with Kislyak, and Yates said she had "two in-person meetings and one phone call" with McGahn in January to discuss the matter. Yates also briefed Burnham, McGahn's deputy and another aide Mueller wants to interview, on the Justice Department's findings about Flynn.

When Yates told McGahn that Flynn could be subject to Russian blackmail because Russia would've been aware he had misled Vice President Mike Pence about his conversations with Kislyak, McGahn asked her why the department cared if "one White House official lied to another," according to Yates' testimony.

Yates told Democratic Sen. Chris Coons that, in the course of their meetings, "Mr. McGahn demonstrated that he understood that this was serious."

Flynn did not resign until mid-February, following The Post's report and weeks after Yates first warned McGahn about his vulnerability.

McGahn was also a critical part of the process when Trump fired Comey in May, The New York Times reported. Comey's firing prompted the deputy attorney general, Rod Rosenstein, to appoint Mueller as special counsel leading the FBI's Russia investigation. As part of his investigation, Mueller is reportedly looking into whether Trump fired Comey in an effort to obstruct the FBI's investigation into his campaign.

The weekend before officially dismissing the FBI director, Trump put together a draft letter laying out his reasons for firing Comey, with the help of White House aides Stephen Miller, Jared Kushner, and Ivanka Trump.

McGahn reportedly advised Trump against sending the letter to Comey, and marked up the copy he was given to remove and alter certain details that he may have believed to be problematic.

"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" as part of the obstruction-of-justice case he is building, Mariotti told Business Insider last weekend. If he finds out the details of what McGahn said to Trump, Mueller could "say that 'Donald Trump was warned by the White House counsel that this was a problematic step and decided to do it anyway,'" he said.

The substance of what McGahn told Trump is important — and there's no guarantee that it could be withheld as privileged information, because attorney-client privilege does not hold between a government lawyer and a government employee in response to a grand jury inquiry.

If it emerges that McGahn "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," Mariotti said.