President Trump issued a memorandum on April 4, 2018 announcing his decision to deploy the military to the United States-Mexico border to help fight illegal immigration as well as to combat drug trafficking and gang activity. He directed the Attorney General and the Secretaries of Defense and Homeland Security to mobilize the National Guard to assist border authorities. The president cited Title 32 of the U.S. Code has authority for the deployment.
In a report published on April 19, 2018, the Congressional Research Service (CRS) addressed the legal considerations surrounding the president’s authority to deploy the National Guard or armed forces. Under Title 32, National Guard units remain under their state governors’ control. While the military has no legal mandate to deal with immigration issues, Title 32 expands the scope of their undertakings at the border to include “homeland defense activities” that protect the United States from threats or invasion on its soil.
According to the CRS, the Posse Comitatus Act, a post- Civil War statute, prohibits National Guard members under the federal government’s control from performing domestic law enforcement activities pertaining to issues like immigration at the border. Troops are only allowed to function in a supportive capacity by performing tasks such as personnel training or equipment maintenance, as well as participating in some counterterrorism and counterdrug measures.
There is recent precedent for deployment. Former presidents George W. Bush and Barack Obama both used Title 32 to send National Guard troops to the southern border to support U.S. Border Patrol agents and bolster security. Those deployments did not involve direct law enforcement activities, such as conducting seizures at the border or arresting undocumented immigrants and drug trafficking suspects.
The Trump administration has been coordinating the deployment with the governors of California, Arizona, Texas and New Mexico. Between 2,000 and 4,000 troops are expected to be sent to the southern border to indirectly assist Border Patrol agents with stopping illegal immigrants from entering the country.