Homeland Security Secretary Kirstjen Nielsen Resigns

Trump names U.S. Customs and Border Protection Commissioner Kevin McAleenan as acting secretary

Kirstjen Nielsen resigned Sunday as homeland security secretary, adding another challenge for an administration grappling with its core immigration agenda while facing a surge of migrants at the southern border.

Ms. Nielsen met with President Trump and acting chief of staff Mick Mulvaney at the White House on Sunday to discuss immigration and personnel issues, one person briefed on the meeting said. Ms. Nielsen had been blindsided by Mr. Trump’s sudden decision to drop the nomination of Ron Vitiello, a veteran border official, from consideration to head U.S. Immigration and Customs Enforcement, this person said. That, at a time when the agency is wrestling with record numbers of families crossing illegally in search of asylum, prompted Ms. Nielsen to resign, the person said.

Mr. Trump made public Ms. Nielsen’s exit via Twitter on Sunday, thanking her for her service. He named U.S. Customs and Border Protection Commissioner Kevin McAleenan as acting homeland security secretary. Mr. Trump’s defense secretary and interior secretary are also serving in an acting capacity.

In a letter to the president, Ms. Nielsen wrote that “despite our progress in reforming homeland security for a new age, I have determined that it is the right time for me to step aside.”

The 47-year-old Ms. Nielsen had repeated run-ins with the White House during her tenure, and Mr. Trump’s recent threats to close the southern border had spurred warnings from her department that such a move could have a serious economic impact on the U.S., according to several government officials.