Homeland Security Secretary Kirstjen Nielsen is resigning, effective immediately.

Nielsen announced that President Donald Trump accepted the resignation on Sunday afternoon.

“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,” Nielsen said 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.”

U.S. Customs and Border Protection Commissioner, Kevin McAleenan,will take over as Acting DHS Secretary, Trump tweeted.

There are currently more than 4,000 U.S. troops serving at the U.S.-Mexico border; the Pentagon recently announced that it approved a $1 billion transfer in defense spending to the Army Corps of Engineers to build 57 miles of barrier along the border.

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