National Intelligence Director Dan Coats will resign from his post, President Donald Trump announced Sunday.

Rep. John Ratcliffe (R-Texas) is set to replace Coats, a 76-year-old former senator from Indiana and ambassador to Germany under George W. Bush who has long been seen as a major figure in the Republican Party.

Coats’ office is said to have had a tense relationship with Trump, especially following his intelligence assessments regarding Russia, Iran, and North Korea. Trump famously called him and other top intelligence officers “passive and naive” in a tweet earlier this year in which he voiced his disagreement with them and their conclusions about these threats and in which he said he believed the intelligence officials should “go back to school.” He follows other recently departed White House officials, like former Defense Secretary Jim Mattis, in leaving the administration due to alleged severe disagreements with it on major issues.

“I would like to thank Dan for his great service to our Country,” Trump simply wrote on Twitter about Coats.

Coats, who started his role as director of the United States’s vast network of spy agencies in March 2017, remained firm throughout his tenure in defending several American intelligences agencies’ — including the FBI, CIA and NSA — assessments that Russia intervened in the 2016 election to help Trump’s campaign. The White House repeatedly attempted to dismiss Coats’ concerns regarding Russian meddling in the American political system.

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Coats held onto that view in the weeks leading up to Trump’s summit with Vladimir Putin in Helsinki, Finland in July 2018, where Trump infamously said he believed the Russian leader over the American intelligence community’s conclusions regarding Russian meddling in the 2016 election. Coats also warned of the possibility of Russian interference in last year’s midterm elections through dissemination of conspiracy theories and other fake news about liberal candidates online, something that also actually occurred.

Last year, Coats also responded to speculation that Trump could one day invite Putin to the White House for a second one-on-one by sarcastically saying, “That is going to be special.”

Trump reportedly responded to this statement by suggesting Coats was disloyal and said he should step down as intelligence director. However, Vice President Mike Pence, the former governor of Indiana, reportedly defended Coats.

In January, Coats also delivered a presentation on global security threats that ran contrary to Trump’s opinions in many respects, another move that drew the ire of the president.