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 said Kevin McAleenan, the current commissioner of U.S. Customs and Border Protection, would serve as acting secretary.
"Secretary of Homeland Security Kirstjen Nielsen will be leaving her position, and I would like to thank her for her service", the president said.
Nielsen took over the position in December 2017 after John Kelly left the post to become the president's chief of staff.
The speculation is so widespread as to be conventional wisdom already that Miller is the architect of a purge at DHS and is overseeing implementation of Trump's desire to crack down on immigration and the border; As Trump put it, to go in a "tougher direction".
President Trump announced the departure of his homeland security secretary last night after months of arguments about how to fortify the southern border.
Miller's objection to Nielsen may have been that while she was game to inflict as much punishment as legally allowable on Central American refugees who crossed the US border, she hesitated to flout the law or tank the economy in order to fulfill the Trump agenda.
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Nielsen told Trump that would be a bad and even unsafe idea, and that the governor of Texas, Republican Greg Abbott, has been very supportive of the President.
On the other side, Republican Senator Lindsey Graham said Nielsen "did her best to deal with a broken immigration system and broken Congress".
Nielsen's exit marks the end of a hard relationship with her boss, who was said to be unhappy with her performance despite her unswerving loyalty and full-throated defence of the president's most controversial policies.
Her tenure was marked throughout by tensions with Trump, who reportedly lashed out at her several times because illegal border crossings have not been stopped. She was heckled in restaurants as the policy came under criticism. CNN's Jake Tapper reports that Nielsen's status is still unclear as of Sunday evening.
So who will Trump select to fulfill his vision at the border, which may include bringing back the family-separation policy?
Last year, Nielsen came under increasing pressure by critics to step aside after the Trump administration adopted the policy of separating migrant children from their parents as part of its "zero tolerance" approach meant to deter families from leaving home in the hope of entering the United States.
The role didn't gain her popularity, but it helped her gain enough of Trump's trust to elevate her to the Cabinet post.
Ultimately, acting White House chief of staff Mick Mulvaney seemed to have been able to talk the President out of closing the port of El Paso. "And the problem is, the nature of the crossers, of migrants, coming across the border has changed", said York.