Department of Homeland Security Secretary Kirstjen Nielsen will be leaving administration

Department of Homeland Security Secretary Kirstjen Nielson will be leaving her position, President Donald Trump tweeted Sunday.

Trump also tweeted that Kevin McAleenan, the current U.S. Customs and Border Protection commissioner, will become the acting secretary for DHS.

Nielsen was scheduled to meet with the president at 5 p.m. in the White House residence about border security, but sources told ABC News that the meeting turned into a discussion about Nielsen’s future.

A veteran of the George W. Bush administration, Nielsen had been chief of staff to then-Homeland Security secretary John Kelly before he became Trump’s chief of staff at the White House.

Nielsen was a close ally and confidante of Kelly, who left the administration at the end of 2018, marking a dramatic shift in the power dynamics of the West Wing, and there was continuing tension between Trump and Kelly over how the president treated her.

At the helm of DHS, Nielsen was a major player in implementing the administration’s highly controversial “zero-tolerance” policy that resulted in the separation of thousands of migrant children from their parents during the summer of 2018.

Nielsen became the public face of the policy, and at one point, was targeted by protesters who heckled from a few feet away while she dined at a Mexican restaurant in Washington, D.C.

“To a select few in the media, Congress and the advocacy community, I’d like to start with a message for you: this department will no longer stand by and watch you attack law enforcement for enforcing the laws passed by Congress,” Nielsen said in June 2018, defending the policy while speaking to the National Sheriffs’ Association in New Orleans.

Known as a cybersecurity policy wonk, Nielsen saw Homeland Security through a successful 2018 midterm elections amid concerns over cyber attacks. She had repeatedly said Russia was to blame for meddling in the 2016 presidential elections while not explicitly supporting special counsel Robert Mueller’s investigation into Russian interference.

Trump nominated Nielsen to be DHS secretary in October 2017. She was sworn in as DHS secretary in December 2017.