Texan Rex Tillerson, who last summer referred to President Trump as a “moron,” received the presidential boot from his job as U.S. secretary of state today, with a Trump tweet that he will be replaced by CIA director Mike Pompeo.

Tillerson, the former head of Exxon with experience negotiating international business deals, has clashed repeatedly with the president. Most recently, it was over talks with North Korean leader Kim Jong-un. As conditions between the United States and North Korea grew more bellicose last year, Tillerson reached out to officials in Pyongyang, hoping to start a new dialogue. Trump publicly belittled Tillerson on Twitter. “I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man,” Mr. Trump wrote.

Then recently, Trump did one of his famous policy pirouettes by agreeing to a request to meet personally with Kim. Diplomatic circles around the globe cringed at the idea that Trump would personally negotiate with Kim without extensive preparation for the talks. Tillerson tried to calm the waters last Friday during a trip to Africa by telling reporters that there is a distinction between “talks” and “negotiations.” Tillerson said Trump had been open to “talks” with Kim and decided on Thursday that “the time was right.”

In his usual style, Trump announced Tillerson’s ouster on Twitter without explanation.

Tillerson had been talked out of resigning by Vice President Mike Pence last summer after a series of policy clashes with the president. People in attendance at one cabinet meeting told journalists that Tillerson left the meeting and openly called Trump a “moron.” Several days later, Trump delivered a politicized speech to the Boy Scouts of America, an organization that Tillerson once headed. Tillerson declined to confirm calling the president a name or that he had considered resigning, and Trump announced he had “total confidence in Rex.”

Tillerson had urged the president to stay in the Trans-Pacific Partnership and the Paris climate accord, positions the president rejected. With little direct foreign policy experience and often contradicted by Trump, Tillerson floundered in the job of secretary of state. After Trump withdrew from the trade deal, Tillerson said he was still studying participation. He contradicted Trump on climate change during a hearing before a U.S. Senate committee. “My view didn’t change,” Tillerson told committee members. “My views were heard out. I respect that the president heard my views, but I respect the decision he’s taken.”

Diplomacy sometimes is as much about what you don’t say as about what you do say. Tillerson just came off repeatedly looking like an administration official who was uncomfortable with the administration and president he was supposed to be representing.

The selection of Tillerson was unusual from the start because he had no experience in government. A graduate of the University of Texas at Austin with a degree in engineering, Tillerson joined Exxon in 1975. In 1995, he was named president of Exxon Yemen Inc., and rose to serve as the chairman and chief executive of ExxonMobil from 2006 to 2017. On behalf of Exxon, Tillerson made business deals with Russian president Vladimir Putin in 2014 and opposed sanctions against Russia. Closer to home, Tillerson made national news as the head of Exxon in 2014 when he opposed a hydraulic fracturing well that was being drilled near his Denton County home.