Kevin McAleenan, who has been tapped to take over Nielsen's job on a temporary basis, moves into his new digs, there won't be a Senate-confirmed leader at Customs and Border Protection, either.

Miller has always had a strong hand in the administration's internal wars over immigration policy, but now there's no one left to fight him.

"Stephen Miller's fingerprints are all over Secretary Nielsen's resignation letter," said Dan Eberhart, a major Republican donor who is in touch with administration officials. "Trump wants to double down on the immigration strategy and Nielsen was apoplectic at the idea of closing the border."

That letter reads as an explanation of Trump's lurch to a more aggressive crackdown on immigration in the aftermath of his failure to use a government shutdown to force Congress tovalues," she wrote.

Her message, in short: that Trump has done everything he can to stop undocumented immigrants from coming into the United States and Congress is to blame for any shortcomings on that front.

At a time when Trump is teeing up a "promises made, promises kept" re-election slogan, that's the way he's choosing to frame the fact that his border policy hasn't yet produced the wall he promised to build along the border, hasn't stemmed the tide of immigrants seeking to cross into the U.S., and hasn't addressed the humanitarian crisis — overflowing detention centers, medical needs and an inability to process asylum-seekers — that didn't exist when he first proposed the wall.

Trump had a crisis in confidence with regard to Nielsen, but the humanitarian emergency at the