Hundreds of protesters flooded the lobby of Trump Tower Thursday to denounce the arrest of Mahmoud Khalil, a Palestinian activist detained by ICE over his involvement with pro-Palestinan demonstrations at Columbia University.

Rubio’s letter notified DHS that he had revoked both targets’ visas, setting in motion plans for U.S. Immigration and Customs Enforcement to arrest and attempt to deport them, according to a senior DHS official and another U.S. official who spoke on condition of anonymity to describe how the operation against Khalil took shape.