President Trump said late Friday that he was replacing Kevin McAleenan, the acting secretary of the Department of Homeland Security, after a tenure where McAleenan lowered border crossings but clashed with other senior immigration officials and struggled to earn the trust of the president.
Mr Trump said he will be announcing a new acting secretary in the next week.
"Kevin now, after many years in government, wants to spend more time with his family and go to the private sector", Trump posted minutes before he was supposed to appear at a campaign rally in Louisiana.
Shortly following the president's announcement, McAleenan issued a farewell statement on Twitter, thanking Trump for his support. Trump said he'd name a replacement in the coming week, the fifth leader of DHS in two years.
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In an interview with The Washington Post published on October 1, McAleenan - whom Trump never formally nominated for the Cabinet position - said that while he controls his department, "What I don't have control over is the tone, the message, the public face and approach of the department in an increasingly polarized time".
Before becoming acting secretary, Mr. McAleenan served as commissioner of U.S. Customs and Border Protection, one of the agencies operating under the Department of Homeland Security (DHS). "The El Paso shooting hit close to home", the source said, noting that six of those killed were family members of five agents and officers who work for the Department of Homeland Security.
"He did his best as a professional public servant but those qualities are not prized in this administration", said Bersin, an assistant Homeland Security secretary for worldwide affairs and Customs and Border Protection commissioner under Obama.
Although McAleenan was not a member of Trump's inner circle - he is a career civil servant and Democrat - or a frequent presence on television like others in the department, he was respected by the White House for his efforts, and his departure came as something of a surprise.
The president's signature issue makes the department his focus and his ire, and balancing a White House eager to push major changes with the reality on the ground is a constant challenge. "That may be why he's no longer there", he said.