President Trump floated the idea Tuesday of deploying troops to the U.S.-Mexico border.

“Until we can have a wall and proper security, we are going to be guarding our border with our military,” Trump said at the White House.

He continued: “That’s a big step, we really haven’t done that before, or certainly not very much before.”

That’s not exactly true. Long-standing concerns about the security of the southern border, cited by Trump, led to National Guard troops being deployed by the thousands under Presidents Barack Obama and George W. Bush.

On Wednesday, the Trump administration followed through, announcing that it will send National Guard troops to the border as part of a larger crackdown on illegal immigration.

As The Post’s Seung Min Kim reported, administration officials “disclosed few specifics about the planned deployment — such as how many troops will be sent to the border, how long they will be stationed there and what their tasks will be — citing ongoing discussions” with the border-state governors who oversee their respective National Guard operations.

But Homeland Security Secretary Kirstjen Nielsen pledged that the size of the troop deployment will be “strong” and “as many as is needed to fill the gaps that we have today.”

As The Post reported:

Under Trump’s plan, National Guard troops will assist Border Patrol agents until Congress passes legislation to deal with what the administration says are legal loopholes in immigration enforcement, according to an official familiar with the plan. The official, who would discuss the unreleased details only on the condition of anonymity, said the troops are expected to be in a support role, conducting tasks such as road development and intelligence gathering.

Here’s how two of Trump’s predecessors deployed National Guard personnel on the southern border.

Operation Jump Start, President Bush, 2006-2008

At the height of the war in Iraq and months before a troop surge there, Bush federalized 6,000 National Guard troops in California, Arizona, New Mexico and Texas. Another battle, across the border in Mexico, was simmering as Mexican officials declared war on drug cartels in late 2006, sparking waves of killings and instability that threatened spillover.

Despite the presence of armed U.S. soldiers and airmen, their mission was mostly passive, Customs and Border Patrol said. The Posse Comitatus Act forbids using the military for domestic law enforcement outside military bases, leaving troops focused on conducting surveillance from ground stations and helicopters, installing fences and vehicle barriers and training.

Troops were typically expected to avoid capturing suspected drug traffickers or undocumented migrants and instead report activity to federal agents, but orders that activate troops to the border affected what military personnel could do.

Under Title 10 for instance, Guard troops are under the command of the secretary of defense, using federal funds. Troops activated under Title 32 are federally funded but are under the command of the state governor, where they have more flexibility for law enforcement operations.

Officials said at the time that it was a necessary augmentation that allowed agents to pivot from administrative and infrastructure tasks and focus on ground operations.

But the $1.2 billion price tag raised questions about the use of troops to fulfill a Department of Homeland Security mission, as National Guard troops were exhausted from rotations in Iraq and Afghanistan.

There also were tensions on the border after a deadly 1997 incident involving the military. A U.S. Marine shot and killed an American high school student carrying a .22 rifle who was mistaken for a hostile person as he herded goats at the Texas border, leading to a temporary halt of military activity there.

DHS pointed to successes, including large drug seizures and an incident in which Guard troops dived into the Rio Grande to save a Central American migrant from drowning.

Operation Phalanx, President Obama, 2010-2016

The successor to Jump Start began with an Obama authorization to deploy 1,200 troops along the border, again amid fears that violence would spread on the U.S. side after high-profile killings north of the border, The Post’s Nick Miroff reported in 2011.

Another reason: Customs and Border Protection agents needed time to fill their ranks following staffing shortfalls.

National Guard troops deployed a fleet of UH-72 Lakota helicopters later in the mission with infrared camera arrays to detect movement from the sky at night and through some of the foliage migrants use as concealment.

A release from the Guard said the helicopters typically included a Border Patrol agent on board. The Lakotas used powerful radio equipment that helped agents communicate with one another and Guard units spread over vast areas.

The Guard touted the deployments as a way for troops to get hands-on experience in the mission, which cost $110 million in 2010, its first year.

But the Government Accountability Office issued a report in 2011 detailing Pentagon concerns about the lack of strategy for troops plugged into an ongoing, permanent mission executed by DHS.

The spectrum of how troops could operate depending on their orders left DHS struggling to figure out how to best utilize them, the report found.

There were other government worries.

“Department of State and DOD officials expressed concerns about the perception of a militarized U.S. border with Mexico, especially when State and Department of Justice officials are helping support civilian law enforcement institutions in Mexico to address crime and border issues,” the report found.

The Federal Aviation Administration also said it had concerns that unmanned drones would be able to detect and avoid other aircraft operating near the border.

In late 2011, Obama scaled back the mission to focus on aerial surveillance.

Other notable deployments occurred during this period. In 2014, then-Gov. Rick Perry (R) dispatched about 1,000 Texas National Guard troops to the southern border after an influx of unaccompanied minors from Central America seeking asylum in the United States. Air Force bases were used as temporary shelters for the children.

This post, originally published on April 4, has been updated.

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