“I’ve said it before, and I am saying it again: firing the special counsel is a red line that the president cannot cross,” Warner said in a statement. “Any attempt to remove the special counsel, pardon key witnesses, or otherwise interfere in the investigation, would be a gross abuse of power, and all members of Congress, from both parties, have a responsibility to our Constitution and to our country to make that clear immediately.”

The news of the June showdown once again places McGahn at the center of attention, an unusual (and likely uncomfortable) role for a White House counsel. McGahn came to the White House after serving as Trump’s campaign lawyer, but he has an unusually GOP-establishment resume for a Trump aide. (McGahn, with long hair and a side gig in a rock band, has always been a bit apart from the establishment, too.)

McGahn’s office has been central to several key developments in the Russia saga. According to an NBC News report this week, McGahn was the first White House official to learn of Flynn’s January 24 interview with the FBI. That interview would prove cataclysmic. Flynn lied to FBI agents about his contacts with the Russian ambassador, eventually leading to a December 2017 guilty plea and an agreement to cooperate with Mueller. NBC said Flynn did not tell McGahn about the interview, and McGahn learned about it from Acting Attorney General Sally Yates. Flynn also lied to Vice President Pence, which precipitated his dismissal in February. Trump, in turn, asked Comey to lay off of Flynn, one of several encounters that escalated to Comey’s firing—and, by extension, Mueller’s appointment. Trump’s conversations with and eventual firing of Comey also form the basis for a presumed investigation into whether Trump obstructed justice in the Flynn case.

When Trump decided to fire Comey, according to a earlier report in the Times, a former career Justice Department lawyer now working in McGahn’s office named Uttam Dhillon thought such a dismissal would be catastrophic and tried to convince the president that he did not have the authority to fire the FBI director. Later research proved that the president did have such authority, though Dhillon’s prediction about political fallout has proven accurate. Unsurprisingly, Mueller has shown an interest in McGahn’s office. McGahn himself has been interviewed twice, and eight members of his office have spoken to the probe, according to the White House.

McGahn’s bold decision to defy Trump may well have saved the president from himself. It is tempting to wonder whether McGahn could have saved Trump even more headaches if he had dissuaded him from firing Comey a month earlier by threatening to resign then. Yet hindsight here is less than 20-20: Comey would have remained head of the FBI and head of the investigation into Russian interference in the election, and might have been just as dogged in pursuing it as Mueller has been. Nor does anyone besides the president have a firm grasp on what Mueller might find.

It is up to Mueller to decide whether Trump’s actions merit a charge of obstruction of justice, but for Congress and the public, the central question remains what it is that has made Trump so anxious to suffocate the probes examining his campaign, presidency, and finances.