Hundreds of thousands of students and others have signed petitions claiming that Mahmoud Khalil’s arrest violates his rights of free speech.

The Trump administration has arrested and decided to deport Mahmoud Khalil, a green card holder, married to an American citizen who is eight months pregnant. His arrest raises important questions relating to the status of permanent residents who have green cards.

The law explicitly authorizes their deportation on a number of specified grounds, including conviction for crimes of moral turpitude, as well as for somewhat vaguer “national security” grounds.