Homeland Security Secretary Kirstjen Nielsen testifies before the House Homeland...

Homeland Security Secretary Kirstjen Nielsen testifies before the House Homeland Security Committee in March. Credit: The Washington Post / Jahi Chikwendiu

WASHINGTON -- Homeland Security Secretary Kirstjen Nielsen stepped down from her post on Sunday, a move that comes two days after President Donald Trump visited the U.S. and Mexico border promising his administration would be “tougher” on immigration enforcement.

“Secretary of Homeland Security Kirstjen Nielsen will be leaving her position, and I would like to thank her for her service,” Trump said in a tweet that followed a private meeting with Nielsen at the White House on Sunday.

Trump in a follow-up tweet named Kevin McAleenan, the current U.S. Customs and Border Protection commissioner, as acting secretary of the Department of Homeland Security. The agency, established in the wake of the 9/11 terrorist attacks, is tasked with bolstering the nation’s security infrastructure on multiple fronts including cybersecurity, election security, and border enforcement.

Nielsen tweeted out her resignation letter about an hour after Trump’s post, saying she “worked tirelessly to advance the goals and mission of the Department.” Sunday evening, she tweeted that she had agreed to stay on until Wednesday "to assist with an orderly transition and ensure that key DHS missions are not impacted."

Her departure marks the end of a rocky tenure that started in December 2017 when she was confirmed to replace her mentor John Kelly, who left his post leading the department to become White House Chief of Staff. 

Trump often complained to White House officials that Nielsen was too soft on immigration, reportedly blaming her for an uptick in illegal border crossings.

Meanwhile, immigration groups and congressional Democrats often denounced Nielsen for enforcing Trump’s hard-line immigration policies such as the “zero-tolerance” border apprehension policy that led to the separation of thousands of migrant minors at the southern border last year.

Last week, in a federal court filing, Trump administration officials said it could take up to two years for the federal government to identify thousands of children separated from their families as part of a federal lawsuit that seeks the reunification of all separated families.

Nielsen’s exit comes days after Trump withdrew his nomination of Ronald Vitello to serve as Immigration and Customs Enforcement director, citing the desire to “go in a tougher direction.”  Vitello had served as acting director since last June when Thomas Honan retired.

McAleenan’s promotion to acting secretary makes him among the several members of Trump’s cabinet working in an “acting” capacity. The departments of Defense, Interior, Small Business Administration, Office of Management and Budget, and White House chief of staff all have acting heads.

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