The addition of longtime Washington, D.C., lawyer Emmet Flood to President Trump’s legal team on Wednesday marks a major win for another top legal adviser to the president who has, for months, been operating in the Trumpland version of Siberia.

White House Counsel Don McGahn was chiefly responsible for orchestrating Flood’s hiring and was thrilled when it was formally completed, according to four sources inside and outside the West Wing. That’s in large part because Flood provides McGahn with two things he’s long coveted: an ally on the legal team handling the Russia probe and a potential successor for his own post, which Flood, as part of this arrangement, will be granted in due time.

There is no set date for McGahn’s exit from the White House. But for months now, his position in the administration has been shaky as his relationship with Trump has deteriorated.

Though McGahn is in the room for meetings involving high-profile legal matters (EPA Director Scott Pruitt’s ethics foibles, the Iran nuclear deal, and so on) the two hardly talk directly to each other anymore. One White House official conceded that they are “barely on speaking terms” unless they absolutely have to be.

Part of tension is intrinsic. The president and McGahn have vastly different personalities and interests. A longtime GOP lawyer who once chaired the Federal Election Commission, McGahn has never sought to be, as one source close to him characterized, a “shoot-the-shit” kind of adviser the way so many other West Wing officials have become in order to stay in Trump’s good graces.

Though he worked as the lawyer on Trump’s 2016 campaign, “he doesn’t speak ‘Trump,’” another outside adviser close to Trump and McGahn said. “Never has.”

Another factor in the chasm between the two men has been special counsel Robert Mueller’s investigation into Russia’s interference in the 2016 election. McGahn has bristled at the accommodating approach that Ty Cobb—the lawyer Flood is replacing—often championed.

But McGahn also ruffled feathers with the president over his more combative posture. The relationship between the two plummeted shortly after The New York Times published a story in January on how the president backed off of demanding Mueller’s firing after McGahn threatened to resign over such a move.

According to three administration officials, the president subsequently vented about the Times story to McGahn’s face in a tense Oval Office meeting that included White House Chief of Staff John Kelly. During the meeting, which was first reported by the Times, McGahn and Trump argued about whether the president had actually, technically ordered the sacking of Mueller. McGahn had already rebuffed Trump’s earlier attempt to get him to issue a public statement denying the veracity of the January article published by the Times. And during the meeting in the Oval Office, he reaffirmed that he would not issue a statement knocking down the story.

McGahn “would not lie about it and put his name to it in public,” as one senior Trump aide put it.

According to multiple sources familiar with this episode and the aftermath, what little was left of the personal relationship between Trump and McGahn cratered at that point. Incensed by the White House counsel’s decision, the president would later wonder aloud to close associates if McGahn himself had leaked the initial Times report and if McGahn could be trusted in general.

Presidents have had difficult relationships with their White House counsels in the past. But rarely, if ever, have tensions arisen to the extent that the two parties are operating at a distance.

“Deploying the silent treatment against your White House counsel, particularly when you’re dealing with a host of legal issues and tensions with the Justice Department, is not a well-thought-out strategy,” Ben LaBolt, a former Obama spokesman who dealt with judicial matters for his press team, told The Daily Beast.

But the Trump administration is sui generis in its operational structure. While the Trump-McGahn relationship may be unconventional, it also is a reflection of the broader disorder that has marked much of the White House’s legal structure—a disorder that Flood now must try to get control over.

It is a difficult task, one that has befuddled McGahn himself. But whereas others have left, the White House counsel has persisted in his post. He has done so partially because he is somewhat walled off from the Russia probe (being a witness to a potential act of obstruction) and partially because he has focused his efforts on other consequential matters.

More than anyone else inside the administration, McGahn is chiefly responsible for the robust effort to stack the judiciary with young, conservative judges.

“President Trump campaigned on the promise to appoint judges in the mold of Justice Scalia and Justice Thomas, and Don McGahn has been instrumental in carrying out that promise,” said Carrie Severino, chief counsel and policy director of the Judicial Crisis Network. “The fact that President Trump has appointed a record number of extraordinarily qualified judges so early in his presidency, on top of appointing Justice Gorsuch, is a testament to the work done day-in and day-out by Don McGahn and his team.”

McGahn’s efforts to overhaul the courts have been so aggressive that, at times, it has rankled Republicans on the Hill who occasionally have been openly critical of the quality of nominees he has sent to the Senate. But he is largely considered a driving force behind the most consequential element of the Trump presidency—a fact that makes the discomforts with the president bearable.

As Hans von Spakovsky, a senior legal fellow at the conservative Heritage Foundation, simply noted, “Don McGahn has been key.”

—With additional reporting by Betsy Woodruff and Lachlan Markay