announcedhe will replace national security adviser H.R. McMaster with former United States Ambassador to the United Nations John Bolton.

The president wrote in a tweet that Bolton, the hawkish former Bush administration official, will take over for McMaster on April 9 .

“I am pleased to announce that, effective 4/9/18 , @AmbJohnBolton will be my new National Security Advisor. I am very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend. There will be an official contact handover on 4/9,” Trump wrote.

I am pleased to announce that, effective 4/9/18, @AmbJohnBolton will be my new National Security Advisor. I am very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend. There will be an official contact handover on 4/9.

McMaster, a three-star Army lieutenant general, will retire from the military, a White House official said. The general has been discussing his departure with Trump for some time and both men decided to make his exit official now because the constant speculation about his job status was interfering with his duties, according to the White House.

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Trump is dealing with a number of high-stakes decisions, including planned talks with North Korean leader Kim Jong Un and an upcoming deadline to extend sanctions relief under the Iran nuclear deal.

Bolton, who has worked as a Fox News analyst and at the conservative American Enterprise Institute, has been an informal adviser to Trump. He was spotted walking in the West Wing on Thursday afternoon hours before his hiring was announced.

Bolton appeared on Fox News on Thursday evening shortly after the news broke, saying he did not expect the decision to be made official so soon.

“It’s still sinking in, so I haven’t thought about it a great deal," he told host Martha MacCallum when asked what getting the job means to him.

Trump’s decision to bring Bolton aboard signals he is seeking to move to the right on national security issues. Both Tillerson and McMaster were seen as moderates and both men urged Trump not to scrap the Iran deal. Tillerson also supported talks with North Korea to resolve the crisis over its nuclear program.

Pompeo, like McMaster, is seen as a national security hawk.

The president decided to replace McMaster following months of friction between the two men. Trump publicly scolded McMaster in February after his national security adviser said there was "incontrovertible” proof that Russia meddled in the 2016 election.

“General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians and that the only Collusion was between Russia and Crooked H, the DNC and the Dems,” Trump tweeted at the time.

Trump hired McMaster in February 2017 to replace Michael Flynn, who was fired for lying to Vice President Pence and other senior officials about his conversations with Russia's ambassador to the U.S.

McMaster pushed out a number of hard-line officials Flynn had hired on the National Security Council, irking Trump allies who complained that the moves undermined the president's ability to carry out his agenda.

McMaster, a detail-oriented military strategist, also struggled to build a personal relationship with the freewheeling Trump. Multiple reports have noted that Trump often scoffed at the general’s lengthy briefings on foreign-policy subjects.

White House press secretary Sarah Huckabee Sanders recently sought to tamp down that McMaster’s ouster was imminent.

“Just spoke to @POTUS and Gen. H.R. McMaster — contrary to reports they have a good working relationship and there are no changes at the NSC,” she tweeted last Thursday.

White House officials said the decision for McMaster to leave was mutual and that the two men are on good terms. They said it was not related to one moment or incident, an apparent reference to a damaging leak of information from briefing papers for Trump’s call to Russian President Vladimir Putin this week, in which the president congratulated the Russian leader on his recent reelection.

“I am thankful to President Donald J. Trump for the opportunity to serve him and our nation as national security advisor,” McMaster said in a statement Thursday. “I am grateful for the friendship and support of the members of the National Security Council who worked together to provide the President with the best options to protect and advance our national interests.”

In a statement distributed by the White House press office, Trump said McMaster’s “bravery and toughness are legendary” and that his leadership “helped my administration accomplish great things to bolster America’s national security.”

John Kelly John Francis KellyMORE Chief of staff, a retired Marine Corps general who pushed McMaster to take the job, called him "a fine American and military officer" who "brought and maintained discipline and energy" on Trump's national security team.

"A true solider-scholar, his impact on his country and this government will be felt for years to come," Kelly said.

The White House had reportedly asked the Army to give McMaster a fourth star, which would have allowed him to transition into a plum military post. Kelly reportedly viewed the move as important to show that fired White House officials can find good work after leaving the building. But that did not happen.

Bolton’s hiring was met with opposition among Democrats on Capitol Hill, who expressed fear that he could help lead the country into an overseas war. As President George W. Bush’s U.N. ambassador, Bolton was a vocal proponent of the Iraq War.

Republicans cheered Trump’s decision.

Updated at 7:25 p.m.