Former Secretary of State Hillary ClintonHillary Diane Rodham ClintonGraham: Trump can make GOP bigger, stronger, or he 'could destroy it' Hillicon Valley: China implicated in Microsoft breach | White House adds Big Tech critic | QAnon unfazed after false prediction Jill Biden redefines role of first lady MORE on Monday said that the Trump administration's treatment of migrants will remain unchanged despite Kirstjen NielsenKirstjen Michele NielsenLeft-leaning group to track which companies hire former top Trump aides Rosenstein: Zero tolerance immigration policy 'never should have been proposed or implemented' House Republican condemns anti-Trump celebrities during impeachment hearing MORE's resignation as Homeland Security secretary.

“Let's be clear: This administration's dehumanization and cruelty toward migrants will not stop after Kirstjen Nielsen leaves office. It is their principal policy," the 2016 Democratic presidential nominee tweeted.

 

Trump announced Nielsen's resignation Sunday, promoting Kevin McAleenan to acting secretary of the Department of Homeland Security.

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Nielsen was the public face of the Trump administration's "zero tolerance" immigration policy that drew widespread criticism last summer.

The policy resulted in thousands of children being separated from their families at the border.

Several commentators and politicians have said that Nielsen will be remembered primarily for her role in that policy.