President Trump will sign a proclamation Wednesday directing the Defense Department and the Department of Homeland Security to work with governors to deploy the National Guard to the southern border. The proclamation was announced by Homeland Security Secretary Kirstjen Nielsen Wednesday.
Trump himself called for using U.S. troops to secure the border with Mexico and prevent illegal immigration Tuesday.
"We're going to do some things militarily," Trump said. "Until we can have a wall and proper security, we're going to be guarding our border with the military."
"That's a big step," Trump continued, "we really haven't done that before, or certainly not very much before."
But the move has many precedents. Every president since Ronald Reagan has called on the National Guard for limited, temporary missions along the frontier.
The troops have been used primarily for activities such as surveillance. They are forbidden from civilian police actions, such as detaining suspects and using force, under a law first signed by President Rutherford B. Hayes in 1878.
The president did not provide details, and his vague remarks appeared to catch many off-guard — including the military. Here are some of the questions raised by the president's comments.
1. How have presidents used troops in the past?
In 1986, Reagan declared drug smuggling a national security threat and launched a multi-pronged approach that included the National Guard, as well as several law enforcement bodies. He also signed a bill that provided amnesty for 3 million migrants who entered the U.S. illegally.
His successors have all called in the troops as well, including George H.W. Bush and Bill Clinton.
George W. Bush deployed some 6,000 National Guard troops in 2006 for what proved to be a two-year mission, assisting the border guards with both undocumented immigrants and drug smuggling.
Obama ordered a similar, if somewhat smaller operation, in 2010. Around 1,200 National Guard troops were called up initially. By 2012, the numbers on the ground were scaled back and a greater emphasis was placed on aerial surveillance.
2. What's the current situation on the border?
After rising for decades, illegal immigration dropped after the 2008 recession that resulted in a sharp decline in economic opportunities.
In addition, the Obama administration deported more than 2 million undocumented migrants, more than any other president. The Obama administration focused primarily on convicted criminals and those apprehended shortly after coming across the border.
Illegal immigration took another downturn when Trump took office last year with his promise to crack down on illegal immigration and build a border wall.
3. So what prompted the president's decision to call on the National Guard?
While illegal immigration remains at a low level compared to past decades, there's been an uptick in recent months, according to figures from Customs and Border Protection.
Critics claim the president is acting more out of politics, noting that the $1.3 trillion spending bill he signed last month did not include the billions he wanted to build a border wall, a fundamental campaign pledge.
Trump has been speaking out — and tweeting — about immigration issues for the past several days, including a claim that "caravans" of migrants are crossing the border. (NPR has fact checked some of those recent claims here.)
4. What is the president planning?
Trump has not detailed his intentions. Homeland Security Secretary Kirstjen Nielsen said Wednesday that the president has directed that the Defense Department and DHS work together with the nation's governors to deploy the national guard to the southern border. She says he will sign a proclamation to that effect.
The troops' presence will be "as many and as strong" as needed to fill gaps they see at the border, she said.
In general, the president can call on the National Guard and the federal government can take command and pay for the troops.
The role of the National Guard or any other troops is limited by the Posse Comitatus Act. President Hayes signed the measure in 1878 with the intent of ending the law enforcement role federal troops were carrying out in the former Confederate states. The troops were supervising elections, chasing down criminal suspects and looking for illegal whisky production.
The law, amended most recently in 1981, does permit the military to do things like help out on U.S. soil in the aftermath of a natural disaster. When it comes to the border with Mexico, this has meant providing surveillance and other support roles.
However, the military cannot act as a police force and make arrests or use force.
Texas Gov. Greg Abbott said Monday a small number of Texas National Guard members would remain on the U.S.-Mexico border, where they have been for the past three years under his authority, conducting surveillance. They will begin taking federal orders this month, he added.
About 100 service members will remain in the border region, The Associated Press reported, citing Lt. Col. Travis Walters, a spokesman with the Texas Air National Guard.