Who is responsible for ensuring the borders against terrorist and other criminals?

The Border Patrol is primarily tasked with securing the borders of a country against illegal activities, including terrorism and criminal enterprises. This agency, which operates under the Department of Homeland Security, plays a critical role in monitoring and controlling the entry of individuals and goods across the borders. Their responsibilities encompass enforcing immigration laws, detecting and preventing illegal border crossings, and responding to threats posed by terrorism and organized crime.

In this context, while local police, the FBI, and Homeland Security all contribute to national security in different capacities, the Border Patrol is specifically dedicated to border enforcement and protection functions. Therefore, when considering the question of who is directly responsible for border security against terrorists and criminals, the Border Patrol's specialized role makes it the most appropriate choice.