"This vindicates what Mahmoud has maintained since day one — that the government cannot detain or deport him based on Rubio’s say-so," Ramzi Kassem, a lawyer for Khalil and a law professor at the City University of New York, said in a statement.

Khalil has been detained since he was arrested in March. The government has argued that the secretary of state can “personally determine” whether he should remain in the country.