Donald Trump’s relationship with John Kelly, his chief of staff, fraught from the beginning, may finally have gone past the point of no return. Two prominent Republicans in frequent contact with the White House told me that Trump has discussed choosing Kelly’s successor in recent days, asking a close friend what he thought about David Urban, a veteran Washington lobbyist and political operative who helped engineer Trump’s victory in Pennsylvania. Ivanka is also playing a central role in the search, quietly field-testing ideas with people. “Ivanka is the most worried about it. She’s trying to figure who replaces Kelly,” a person who’s spoken with her said.

Kelly’s departure likely isn’t imminent, sources said. “He wants to stay longer than Reince [Priebus],” an outside adviser said. Trump can also hardly afford another high-level staff departure, which would trigger days of negative news cycles. “This could be like [Jeff] Sessions,” one of the Republicans explained, referring to Trump’s festering frustration about not being able to replace his attorney general.

But the prospect of a Trump-Kelly rupture became more probable as news of their clashes over immigration leaked. Last week, Kelly reportedly infuriated Trump when he told Fox News that Trump had “evolved” on his position to build a southern border wall. Kelly further catalyzed Trump’s ire when he told Democratic lawmakers that Trump was “uninformed” when he made his campaign promise to build the wall. The next morning Trump rebutted his chief of staff with a tweet: “The Wall is the Wall, it has never changed or evolved from the first day I conceived of it.”

Trump’s anger at Kelly’s immigration comments is the latest flare-up in a relationship that has been deteriorating for months. A four-star marine general, Kelly was never going to be an easy fit in a West Wing with a Lord of the Flies office culture. Staffers have bristled at Kelly’s rectitude, nicknaming him “the Church Lady,” a former official said.

Trump has increasingly been chafing at the media narrative that he needs Kelly to instill discipline on his freewheeling management style. “The more Kelly plays up that he’s being the adult in the room—that it’s basically combat duty and he’s serving the country—that kind of thing drives Trump nuts,” a Republican close to the White House said. In recent days, Trump has fumed to friends that Kelly acts like he’s running the government while Trump tweets and watches television. “I’ve got another nut job here who thinks he’s running things,” Trump told one friend, according to a Republican briefed on the call. A second source confirmed that Trump has vented about Kelly, mentioning one call in which Trump said, “This guy thinks he’s running the show.” (A White House official said “it’s categorically false that Trump is unhappy with Kelly. He’s only ever referred to him as the general, tough, can be rough, and commands respect.”)

Kelly, in turn, has expressed frustration with Trump’s freewheeling management style and habit of making offensive statements. In August, when Trump incited outrage with his Charlottesville comments, Kelly complained to a colleague that he was “holding it together.” The next month, cameras captured Kelly’s infamous facepalm at Trump’s U.N. speech when Trump called Kim Jong Un “rocket man” and threatened to “totally destroy North Korea.” The New York Times reported that Kelly has threatened to quit numerous times.

Trump, for his part, is frustrated that he’s not getting more credit for positive news like the booming stock market and low unemployment numbers. In recent days, he told a longtime friend that the national polls, which put his approval numbers in the low 30s, are under-representing the real number. Trump insisted his approval rating is in the high 50s. The friend challenged him, but Trump didn’t want to hear it. He soon ended the call.