WASHINGTON — More than four months after active-duty troops deployed to southern U.S. states for border security support, congressional Democrats remain unconvinced their presence is needed there.

“Border security is important, but we have other needs in the world,” said House Armed Services Committee Chairman Adam Smith, D-Wash., during a hearing on the topic Tuesday morning. “We also have ISIS and Syria and Russia and China … (The southern border) is not primary to the military’s mission.”

The border support mission, which began shortly before the midterm elections, has been attacked by critics for months as President Donald Trump politicizing both the immigration debate and military personnel.

About 2,300 active-duty service members are currently deployed to the border mission, down from a height of nearly 6,000 last fall. Defense Department officials say the work thus far has cost about $132 million, on top of another $100 million spent on National Guard deployments to support border security missions last year.

On Tuesday, Defense Department officials and Republicans on the Armed Services Committee argued that the military presence along the southern border isn’t improper or even unusual, noting that past presidential administrations have sent troops to assist border patrol agents.

Vice Adm. Michael Gilday, director of operations for the Joint Staff, said the troops’ work has been confined to construction, intelligence and other support roles. Since last fall, the deployments have given Homeland Security agents more flexibility to secure immigration processing centers and strengthened barriers along significant stretches of the southern states.

“(Customs and Border Protection) was better prepared because of the work we did,” he told the committee.

Earlier in the day, acting Defense Secretary Patrick Shanahan said his department would need to send "several thousand" more troops to the border to meet Department of Homeland Security requests for help with the ongoing missions. That would include "additional concertina wire (installation) and then expanded surveillance capability."

So far, that increase has not been approved.

Smith and Democrats on the committee argued that in the past, those same support efforts were successfully handled by National Guard and reserve units. Using active-duty troops instead risks readiness problems, especially since Trump has signaled he intends to keep the service members there for at least another eight months.

Rep. Elissa Slotkin, D-Mich., said the timing of the initial deployment just before the election “makes it hard not to see this as political.”

Rep. Elaine Luria, D-Va., noted that while the president has insisted the troops are needed to block illegal immigrants and drugs from crossing the border, requests for more personnel for drug interdiction efforts by U.S. Southern Command have gone unanswered. “This doesn’t seem consistent with our priorities,” she said.

Other Democrats asked whether the ongoing deployments will hurt overseas missions, routine training and troops’ dwell time.

Gilday said thus far active-duty units have been rotated out every six to eight weeks, in an effort to minimize the impact on those readiness and reset concerns. He said several units will miss company-level training requirements because of the mission, “but we believe we can replace that.”

He also acknowledged the demands for U.S. military forces worldwide but also said the administration has made the southern border a major priority, justifying the deployments.

Part of the reasoning for the rapid deployment of active-duty troops to the region last fall were Trump’s announced concerns over a caravan of immigrants headed from South and Central America to the southern U.S. border.

That group, at one time estimated at more than 10,000 people, largely dispersed before reaching the border, and was largely handled through traditional border security operations.

However, Under Secretary of Defense for Policy John Rood, said military officials are currently monitoring another large caravan amassing in Central America, illustrating the need for the continued active-duty presence along the border. That drew questions from Smith on when, if ever, troops won’t be needed there.

The committee largely avoided discussions about the larger issue hanging over the deployments: Trump’s controversial border wall project and the looming Feb. 15 deadline for a solution to his demands for more than $5 billion for the work.

The president has discussed declaring a national emergency and using military funds to get that money if Congress does not approve the spending. Smith and other Democrats at the hearing again panned the idea, promising a legal challenge if he moves ahead with the plan.

Reporter Aaron Mehta contributed to this story.