Tren de Aragua, a gang born out of a Venezuelan prison, is a loose network that doesn’t operate like groups typically considered terrorist organizations.

On Monday, the Department of Homeland Security announced that it had also revoked the work visa of Brown University professor Rasha Alawieh and denied her reentry into the U.S. after she attended the funeral of Hezbollah leader Hassan Nasrallah in Lebanon.

Debates over President Donald Trump’s hardline migration policies are focused on the Venezuelan gang Tren de Aragua, to some a ruthless transnational criminal organization and to others the pretext for an overhyped anti-migrant narrative.