"In November 2018, Gillibrand was one of eleven senators to sign a letter to United States Secretary of Defense James Mattis concerning "the overt politicization of the military" with the Trump administration's deployment of 5,800 troops to the U.S.-Mexico border and requesting a briefing and written justification from the U.S. Northern Command for troop deployment while urging Mattis to "curb the unprecedented escalation of DOD involvement in immigration enforcement."