Department of Homeland Security's Acting Deputy Secretary Claire Grady has resigned effective tomorrow, a tweet from outgoing Secretary Kirstjen Nielsen said.

The news comes after Secretary Nielsen's resignation on Sunday. The changes at DHS are said to be part of a broader staff change pushed by White House senior adviser Stephen Miller.

Some called into question the legality of Trump tapping Customs and Border Protection Commissioner Kevin McAleenan as acting DHS Secretary.

This is a breaking news story. As more information comes in, this post will be updated.