Kevin McAleenan, the acting secretary of the Department of Homeland Security, is leaving his post, which includes leading civilian agencies on cybersecurity and additional election security responsibilities in working with states.

“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,” President Donald Trump tweeted Oct. 11.

With McAleenan’s departure, the DHS is now poised for its third secretary this year following Kirstjen Nielsen’s departure in April.

DHS’ Cybersecurity and Infrastructure Security Agency, tasked with protecting the country’s critical infrastructure from cyberattacks, spearheads the department’s cybersecurity initiatives. With the cybersecurity threat landscape expanding, sources have told Fifth Domain in the past that part of CISA’s success rests on a secretary who prioritizes cybersecurity. McAleenan’s entire government career was with Customs and Border Protection, where he eventually became commissioner. At a time when DHS is primarily focused on the southern border, McAleenan in recent weeks has publicly shown his backing for CISA.

McAleenan’s immigration background didn’t hamper DHS’ cybersecurity mission, a top CISA official said in recent weeks. Matthew Travis, CISA’s deputy director, said at the agency’s second annual cybersecurity summit Sept. 19 that McAleenan’s took cybersecurity seriously in his role as acting secretary, a role he’s had since last April.

“I can’t tell you how encouraged we were from the get-go at the active engagements he has with us starting on Day One when he took office and every day since then,” said Travis.

His abrupt departure comes just days after he visited CISA’s offices and watched a demonstration of a phishing attack on critical infrastructure. He said in a tweet that the demonstration “showcased the imperative work these security professionals undertake daily.”

McAleenan also recently spoke at CISA’s second annual national cybersecurity summit, where he outlined CISA’s achievements since it was established late last year and emphasized the importance of the agency’s work in protecting critical infrastructure and elections.

“Nation-state adversaries work to identify and exploit technological points of leverage for maximum injury to American critical infrastructure," McAleenan said Sept. 19 at the summit. "Bad actors are using cyber as a means to disrupt and sow discord in our democratic institutions ... That is where CISA comes in.”

On Oct. 10, McAleenan spoke at the U.S. Chamber of Commerce’s annual cybersecurity summit, where he called CISA’s work “unique and critical."

The president said he will announced a new acting secretary next week. Meanwhile, the top ranks of DHS are filled by several unconfirmed, acting officials, prompting Rep. Bennie Thompson — D-Miss., and chairman of the House Homeland Security committee — to call on Trump to quickly nominate someone a permanent secretary.

“The next secretary must be able to convey to the American people that the federal government is focused on keeping the country safe from the top threats we face,” Thompson said in a statement. “We know this includes securing our elections from foreign influence, countering domestic terrorism, and ensuring foreign fighters abroad do not come here.”