Acting Homeland Security Secretary Kevin McAleenan testifies before the House Oversight and Reform Committee on "Trump Administration's Child Separation Policy" on Capitol Hill in Washington, July 18, 2019.

President Donald Trump said in a tweet Friday that acting Homeland Security Secretary Kevin McAleenan is stepping down.

Trump in his tweet congratulated McAleenan on a "job well done" and said he would be announcing a new acting secretary next week. He added that there were "many wonderful candidates."

"Kevin McAleenan has done an outstanding job as Acting Secretary of Homeland Security. We have worked well together with Border Crossings being way down. Kevin now, after many years in Government, wants to spend more time with his family and go to the private sector," Trump tweeted.

"....Congratulations Kevin, on a job well done! I will be announcing the new Acting Secretary next week. Many wonderful candidates!"

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McAleenan took over as acting secretary of the Department of Homeland Security after Trump asked for the resignation of Homeland Security Secretary Kirstjen Nielsen earlier this year. Before that, he had served as commissioner of U.S. Customs and Border Protection.

McAleenan in a tweet thanked Trump for the "opportunity to serve alongside the men and women of the Department of Homeland Security."

"I want to thank the President for the opportunity to serve alongside the men and women of the Department of Homeland Security. With his support, over the last 6 months, we have made tremendous progress mitigating the border security and humanitarian crisis we faced this year...," his tweet said.

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McAleenan walked out of an immigration conference in Washington Monday after multiple attempts to speak over protesters.

McAleenan, who was a keynote speaker at the conference, was met with protesters in the crowd who yelled, "When immigrants are under attack, what do we do? Stand up, fight back!"

Protesters yelled the statement multiple times before McAleenan had a chance to speak at the podium. McAleenan said he would like to discuss the challenges the agency has faced over the past year with the immigration crisis, "above the politics and the daily news cycle." But after persistent shouts, McAleenan walked off the stage without delivering his speech.

The Department of Homeland Security said in a statement: "Unfortunately the Acting Secretary and the audience did not get the opportunity to engage in a robust dialogue this morning due to the disruptions of a few activists."

A Washington Post article said McAleenan had grown "isolated and frustrated" even as "he guided the United States out of the crisis at the southern border."

"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," McAleenan said in an interview with The Washington Post on Oct. 1. "That's uncomfortable, as the accountable, senior figure."

CNBC's Sunny Kim contributed to this report.

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