ICE has been turned into a secret police force. If you'd like a history of the border patrol in the US, then here is an excellent introduction: https://www.youtube.com/watch?v=DdStIvC8WeE
It's not a difficult read, but its authors are leftists and the language may sometimes be difficult for readers with sensitivities related to the goodness of Democrats or Republicans or whatever.
(I think maybe I'll re-read it today as well; it's been a long time.)