On the list of ways Donald Trump’s presidency has no historical precedent, staff turnover ranks at the top. The churn rate in the Trump White House is more than double that of previous administrations, according to one analysis. (It’s triple that of the Obama White House.) Since the inauguration, nearly two dozen senior officials have quit or been pushed out. But even for a White House roiled by firings and resignations, the announcement that Hope Hicks was quitting was of a different magnitude, reaching into Trump’s own bunker in a way no other event has to this point.

The 29-year-old Hicks serves as communications director, but her role and power in the West Wing and in the president’s daily life is vastly more significant than any formal title. She’s been a constant presence at Trump’s side from the inception of his presidential run in 2015, serving as a gatekeeper and emotional support system for the temperamental chief executive. She defends Trump fiercely, and Trump returns the loyalty. Staffers remark that Trump treats Hicks—“Hope-y” as he calls her—like a surrogate daughter. Her centrality was such that it was hard to imagine Trump functioning without her.

But in recent weeks, Hicks became disillusioned with her job, people who’ve spoken with her told me. Her closeness to Trump meant she was also nearest to the hottest flames of the fires that have burned in the West Wing, the most intense being the Russia probe. Hicks has racked up substantial legal fees, one source told me. “She’s in immense personal jeopardy,” one Republican close to the White House said yesterday. “This is a sign the Mueller investigation is a lot more serious than any one of us thought.” (Hicks and the White House declined to comment.)

The tipping point for Hicks was more personal, sources said. She was “emotionally overwhelmed” by seeing herself in the headlines during her boyfriend Rob Porter’s domestic abuse scandal, one Hicks friend told me. Hicks expressed disbelief at the allegations that Porter beat his ex-wives. She’s recently told people she’s no longer dating Porter.

Another factor in her exit was her deteriorating relationship with Chief of Staff John Kelly. “He’s a wartime general and he’s turned the West Wing into a war zone,” the friend recalled Hicks complaining. Kelly blamed Hicks for orchestrating the White House’s defense of Porter, given her personal conflict in the story. According to two sources, in recent days Kelly informed Hicks he wanted Mercedes Schlapp, a senior strategic-communications adviser, to play a bigger role in the press office. “Well, if that’s what Kelly wants, it’s his call,” Hicks said, according to a person who spoke with her. Schlapp, married to Matt Schlapp, head of the American Conservative Union, which runs CPAC, is now a leading candidate for Hicks’s job.

Hicks’s decision to leave is the latest sign of how adept Kelly has been at reversing his own fortunes. Just weeks ago, the chief was on the ropes, his reputation for straight shooting in dire danger. It was revealed he’d promoted Porter even after he knew about the domestic abuse; and it was Kelly who helped blow up immigration-reform talks by calling DACA recipients “lazy.” “You know how Rahm Emanuel said, ‘Never let a good crisis go to waste?’ That’s what Kelly did,” a Republican close to the White House said. But at seemingly his lowest moment, Kelly pulled off a masterstroke by promulgating new security-clearance rules that neutralized his biggest West Wing rivals: Jared Kushner and Ivanka Trump. “The Jivanka team is crumbling,” a person close to the White House said. A day before Hicks resigned, Kushner’s spokesman Josh Raffel announced he, too, was quitting. Between the relentless chaos of the West Wing and the looming Mueller investigation, even the most committed staffers are re-evaluating their options.

As Kelly rapidly consolidates power, Trump thus far shows no signs of reining him in. In recent days, Corey Lewandowski has lobbied the president to fire Kelly, but not yet, a source said. Lewandowski’s advice is that Trump shouldn’t replace him right away, instead holding a series of interviews to find a person he clicks with. Trump rejected the proposal. “He’s too worried about the perception of all the turnover,” the source said.

This article has been updated.