Experts say there has to be a legal basis to revoke a person’s residency status, and removal needs to be ordered by an immigration judge.

A New York federal judge is set to hear pivotal questions in the case of Mahmoud Khalil, a leader of large Gaza solidarity protests at Columbia University who now faces deportation after his arrest by Immigration and Customs Enforcement agents.

Here's a look at what kind of protections foreign students and green card holders have and what might be next for Khalil.