Three Republican-led southern states on Monday (April 9) vowed to send 1,600 National Guard troops to the United States-Mexico border. It’s a direct response to President Donald Trump’s pledge to militarize the border to stem immigration, and it comes as details emerge about the role troops will play in the area.

Per The Associated Press, Texas deployed 250 troops last Friday (April 6), and Governor Greg Abbot said he will add 300 troops per week until the number reaches 1,000. New Mexico expects to send 250 troops to its border, while Arizona officials said the state will deploy 225, followed by another 113 later in the week. 

Arizona Governor Doug Ducey told The AP that the National Guard troop’s mission “is about providing manpower and resources to support federal, state, county, tribal and local law enforcement agencies in stopping the flow of criminals, narcotics, weapons and ammunition that is being trafficked into our state.”

After repeated threats against immigrants and calls for more border security, Trump last week signed a memorandum to deploy troops to the southwest border. The directive reads: 

The Secretary of Defense shall support the Department of Homeland Security in securing the southern border and taking other necessary actions to stop the flow of deadly drugs and other contraband, gang members and other criminals, and illegal aliens into this country. The Secretary of Defense shall request use of National Guard personnel to assist in fulfilling this mission… 

Despite Trump’s claims of a porous southern border, government statistics from 2017 show a dramatic decline in border crossing over the last several years, with arrests along the border plunging to levels not seen since 1971.

Trump’s deployment of National Guard troops follows similar moves by his predecessors. Both George W. Bush and Barack Obama sent troops to the border in response to surges in drug violence and undocumented immigration.

On Monday, new details emerged about the role National Guard troops will play on the border. Their work will include maintenance of roads, providing support for drones and helicopters, and operating surveillance systems. Troops will also assist border patrol agents with arrests of immigrants and carry out armed patrols, according to The Washington Post

“National Guard personnel will only be armed for their own self-protection to the extent required by the circumstances of the mission they are performing,” Lieutenant Colonel Jamie Davis, a Department of Defense spokesman, told The Post.