Secretary of State Marco Rubio said Monday he doesn’t understand “why it’s so hard for some to comprehend” that United States visitors aren’t entitled to a visa.

The Trump administration has experienced various speed bumps in pursuing its deportation agenda, including revoking the visas of pro-Palestinian students who have engaged in protests on college campuses. Last month, a federal judge issued a sweeping ruling entitling noncitizen students who have sued the Trump administration to a court hearing if their immigration status changes.