Homeland Security Secretary Kirstjen Nielsen resigns amid Trump’s growing frustration over border crossings

Homeland Security Secretary Kirstjen Nielsen resigned on Sunday amid President Donald Trump’s growing frustration and bitterness over the number of Central American families crossing the southern border.

Trump announced on Sunday in a tweet that U.S. Customs and Border Protection Commissioner Kevin McAleenan would be taking over as acting head of the department. McAleenan is a longtime border official who is well-respected by members of Congress and within the administration. The decision to name a top immigration officer to the post reflects Trump’s priority for the sprawling department founded to combat terrorism following the Sept. 11 attacks.

“I have determined that it is the right time for me to step aside,” Nielsen wrote in her resignation letter. “I hope that the next secretary will have the support of Congress and the courts in fixing the laws which have impeded our ability to fully secure America’s borders and which have contributed to discord in our nation’s discourse.”

She led the federal agency since December 2017, and was this administration’s third Homeland Security secretary. A protege of Kelly’s, he brought her to the White House after Trump named him chief of staff. She earned a reputation as an enforcer working to corral the chaotic West Wing.

Nielsen, 45, previously served as a special assistant to President George W. Bush and worked for the Transportation Security Administration.

She rose through the Trump ranks quickly — joining the transition team after the election to help guide Kelly through the confirmation process. She quickly became a trusted aide to Kelly, and the two worked together to impose order on a dysfunctional White House that lacked clear lines of command.

House Homeland Security Committee Chairman Bennie Thompson, D-Miss., said her tenure was “a disaster from the start.” The policies she helped create “have been an abysmal failure and have helped create the humanitarian crisis at the border.”

His Senate counterpart, Sen. Ron Johnson, R-Wis., said the government needed “steady, informed and effective leadership in the administration and in Congress to have any hope of fixing our out-of-control border security and immigration problems.”

Associated Press writers Jill Colvin and Lisa Mascaro contributed to this report.

This story corrects the month in which border agents are on track to make 100,000 arrests and denials of entry to March, not this month.