Mattis tells troops who were rushed to the U.S.-Mexico border: Their mission is TBD

Reporting from Washington —  When a young soldier in Texas asked Defense Secretary James N. Mattis on Wednesday whether his unit would soon be ordered to remove the razor wire and vehicle barriers they had installed at Mexico border crossings, Mattis couldn’t answer.

“Good question. We’ll let you know,” Mattis replied, according to video of the encounter. “Right now, the mission is put them in.”

Asked by another soldier to explain the goals of the border deployment, Mattis said, “Short term, get the obstacles in. Longer term … it is somewhat to be determined.”

The exchanges, during a visit by Mattis and Secretary of Homeland Security Kirstjen Nielsen to a muddy military encampment near the Texas border town of Donna, captured the uncertainty — and tedium — that surrounds President Trump’s preelection decision to rush troops to the border in the largest such deployment in decades.

Nearly 6,000 Marines and Army soldiers are assisting the Border Patrol in Texas, Arizona and California by strengthening defenses and building temporary encampments near dozens of border entry points. A total of about 7,000 troops may be deployed, officials said.

Critics have questioned the need for active-duty troops when there is no discernible threat. Numerous retired senior military officers have criticized Mattis for approving a deployment that appeared aimed more at stirring up Trump’s supporters before the midterm election than confronting a potential enemy.

During the campaign, Trump had warned at rally after rally of an “invasion” by a caravan of about 5,000 migrants, mainly from Honduras, most of whom are still hundreds of miles away from the border with California, their goal. Trump said the group included human traffickers and other criminals.

Trump now appears to have moved on. He has mentioned the caravan just once since the Nov. 6 election, tweeting the announcement of a policy change aimed at preventing migrants who enter the country illegally from seeking asylum.

About 400 of the migrants were bused this week to the border city of Tijuana. Most reportedly plan to turn themselves in at the San Ysidro Port of Entry and ask the U.S. government for asylum. Three separate smaller caravans of Central American migrants are also moving through southern Mexico, but their destination is unclear.

Mattis did not mention the migrants’ quest for asylum in defending the military operation Wednesday.

“We’re here because of the number of illegals who say they are going to illegally try to cross into our country,” he said.

He deferred to Nielsen when asked whether the migrant threat justified the use of thousands of troops. But he told reporters traveling with him that it is an “obviously moral and ethical mission to support our border patrolmen.”

Until Wednesday, Mattis had issued only terse statements about the deployment, denying last month it was a political stunt.

“We don’t do stunts in this department, thank you,” he said.

Mattis emphasized to troops Wednesday that their mission is to “back up” Customs and Border Protection. “Right now that’s our role, and that’s all our role is,” he said.

“The eyes of the world right now — certainly all of the Americans — are on you,” Mattis told the soldiers, adding that they are part of a “nontraditional” mission.

He demurred when reporters pressed him about the fairness of asking troops to miss Thanksgiving with their families after Pentagon officials have warned for years that their units were overstretched by years of war.

“Welcome to your military,” he said. “It’s on duty.”

He stressed the routine nature of the operation, noting that presidents as long ago as Woodrow Wilson in the early 20th century had dispatched forces to the border to halt incursions.

“The threat then was Pancho Villa’s troops,” Mattis said.

The installation of razor wire and barriers at border crossing points will be completed in a week to 10 days, he said. But the troops will stay through early December and potentially longer if the Department of Homeland Security requests an extension.

Mattis declined to provide an estimate of how much the mission will cost.

By law, active-duty troops are barred from conducting domestic law enforcement, including arrest or questioning of migrants on U.S. soil. Pentagon officials reportedly rejected requests from Homeland Security to authorize troops to conduct crowd control and other duties normally carried out by law enforcement personnel.

Most of the troops will not be armed, although military police units will carry weapons for protection of military personnel, officials said.

Lt. Gen. Jeffrey Buchanan told Mattis and Nielsen in a televised briefing that the border region from San Ysidro to Yuma, Ariz., is being overseen by Marines, including an engineering unit, and an Army military police force. The troops have eight ports of entry to cover, he said.

During the campaign, Trump targeted the migrant caravan at every turn. At rally after rally, he framed the election as a referendum on “the caravan, law and order, and common sense.”

“You’ve got some bad people in those groups. You’ve got some tough people in those groups,” he said at an Oct. 20 rally in Mesa, Ariz. “This country doesn’t want them.”

The same day, Trump told reporters that “a fairly big percentage of those people are criminals,” but offered no evidence to support his claim.

Days before the election, Trump cited video of migrants throwing rocks at authorities in Mexico and suggested U.S. troops might respond with deadly force if they face people throwing rocks.

“They want to throw rocks at our military, our military fights back,” the president said. “I told them to consider it a rifle. When they throw rocks like what they did to the Mexican military and police, I say consider it a rifle.”

A day later, amid concerns that U.S. troops would fire on unarmed civilians, Trump walked back that bit of bluster, saying that troops “won’t have to fire” but that migrants throwing rocks would be “arrested.”

Trump rejected a TV ad from his campaign that focused on economic issues, preferring to run a controversial immigration-focused spot featuring a convicted cop killer who entered the country illegally and images of the caravan of migrants.

But on Wednesday, Mattis emphasized his efforts to tamp down the operation’s political overtones. Pentagon officials initially dubbed the deployment “Operation Faithful Patriot,” but abandoned the name after the election.

“I had given instructions that I did not want this mission put in some arcane terms if what we are doing is laying wire.” Mattis said.

david.cloud@latimes.com

Twitter: @davidcloudLAT