Acting Defense Secretary Patrick Shanahan has approved a Department of Homeland Security request to send about 320 troops to the southern border to support Customs and Border Protection officials, the Defense Department announced Monday.

"In any situation that requires DoD personnel to be in proximity to migrants, DHS law enforcement personnel will be present to conduct all custodial and law enforcement functions, and provide force protection of military personnel."

— Pentagon spokesman Lt. Col. Jamie Davis

The big picture: The number of immigrants arrested or turned away at the southern border has reached levels not seen for years, Department of Homeland Security data obtained by Axios shows. President Trump has directed top officials to execute the most aggressive changes in immigration policy since his inauguration, per Axios' Jonathan Swan. Davis said the extra troop support would cost about $7.4 million through Sept. 30.