BASE CAMP DONNA — Sgt. 1st Class Daniel Micek, a platoon sergeant with the 89th Military Police Brigade, tore open the brown packaging of his MRE.

It was a chicken and noodle dish, one of the more sought-after rations because it came with Skittles. But from the cot outside his platoon’s tent at the Army’s latest forward operating base in South Texas, Micek could almost see the bright orange and white roof of Whataburger, a fast-food utopia 8 miles away but off limits under current Army rules. The desert tan flatbed trucks at the base are for hauling concertina wire, not food runs.

Such is life on the latest front where U.S. soldiers are deployed. The midterm elections are over, along with President Donald Trump’s rallies warning that an approaching migrant caravan of Central Americans amounts to a foreign “invasion” that warrants deploying up to 15,000 active-duty military troops to the border in Texas, Arizona and California.

Instead of football with their families on this Veterans Day weekend, soldiers with the 19th Engineer Battalion, fresh from Fort Knox, Ky., were painstakingly webbing concertina wire on the banks of the Rio Grande, just beneath the McAllen-Hidalgo-Reynosa International Bridge.

Nearby, troops from Joint Base Lewis-McChord in Washington state were making sure a sick call tent was properly set up next to their aid station. And a few miles away, Staff Sgt. Juan Mendoza was directing traffic as his engineer support company from Fort Bragg, N.C., unloaded military vehicles.

Come Thanksgiving, they likely will still be here.

Two thousand miles away, at the Pentagon, officials privately derided the deployment as an expensive waste of time and resources, and a morale killer to boot.

A final cost estimate of the deployment has not been made available. But Defense Department budget officials fret that if the number of troops sent to the border does reach 15,000 — it currently numbers 5,600 — the price tag could hit $200 million, with no specific budget allocation from which to draw.

The last time active-duty troops were sent to the border was in the 1980s, to help with counternarcotics missions. Since then, Trump’s predecessors have relied on the National Guard, which arrived with considerably less fanfare than the convoys of vehicles and tent cities that have sprung up in recent days.

The Defense Department’s fiscal 2019 budget had already carved out funds for fighting the Islamic State group in Iraq and Syria, continuing the endless war in Afghanistan and preparing for a potential conflict with a foreign nation, such as China, Russia, North Korea or Iran.

There has been no money set aside to combat men, women and children who are bound for the U.S. border, many of them fleeing violence or corruption. The troops are tasked with the same types of logistical, support and even clerical jobs that National Guard soldiers sent to the border earlier this year are already doing.

The military’s morale issue is almost as worrisome. The deployment orders last until Dec. 15, meaning the troops will be on the border over Thanksgiving. They will have little to do beyond providing logistical support, unless Trump declares martial law. The troops will not be enforcing U.S. immigration law — that would run afoul of the Posse Comitatus Act of 1878, unless a special exception is made.

“When you give a soldier a real mission, you have less of a morale problem, even if it’s Christmas or Thanksgiving,” said Rep. Anthony G. Brown, D-Md., a former Army helicopter pilot who served in the Iraq War. “But when you send a soldier on a dubious mission, with no military value, over Thanksgiving, it doesn’t help morale at all.”

Two days after the midterms, on Thursday, a platoon of Army engineers in Hidalgo, who were stretching bands of concertina wire on the Texas side of the Rio Grande had ditched the body armor. The decision to wear only their uniforms, canteens, gloves and helmets was simple: It was too hot to wear the armored vests, and the soldiers knew they didn’t need them. And some had already suffered heat exhaustion, just days into their new mission.

Roughly 15 miles away, some 500 troops — a medley of medical units, military police officers and engineers — were settled into a routine at Base Camp Donna. It was named after the adjoining Texas town.

Wedged between a four-lane highway and the U.S.-Mexican border wall, the base is reminiscent of those found in Afghanistan and Iraq in the early 2000s.

As it was at the bases in those early war zones, electricity at Base Camp Donna is scarce except to power lights and communications gear. The soldiers have installed a small shower tent. Men and women have set hours for bathing. Permitted shower length: seven minutes.

There is no mess hall — just the MREs.

The Army is setting up another outpost in an abandoned furniture store in nearby Weslaco and is eyeing a spot in Brownsville.

Unlike in Iraq and Afghanistan, the troops do not receive extra combat pay. Nor is there hostile fire pay, since the troops will not be interacting with the migrants.

Officially, Pentagon leaders said their duty was to follow the orders of the commander in chief, not to tell him how he can deploy U.S. troops.

“It’s not my role to make those assessments,” Army Secretary Mark Esper said Wednesday. “We all recognize that one of the many missions of the military is defense of the homeland and security of our borders.”