Washington(CNN) Acting Secretary of Defense Pat Shanahan said Wednesday that the Pentagon was trying to determine how long US troops would be required to support security on the southern border, saying, "We really need to get back to our primary missions and continue to generate readiness."
"This is an issue that (Chairman of the Joint Chiefs of Staff) Gen. (Joseph) Dunford and I work on quite a bit because the question that he and I are really trying to answer is how long will we be at the border," Shanahan told lawmakers at a House Appropriations hearing on the defense budget.
Shanahan indicated that the military is required at the border due to a shortage of Customs and Border Protection personnel, saying "they're thousands of people short."
"We've initiated a set of actions to really understand how many people are they short because we need to get that into a sustained environment, we're driving buses, we're serving food, we're doing medical support, we're doing logistics support. For now, we haven't degraded any readiness but we really need to get back to our primary missions and continue to generate readiness," he added.
Currently, there are 3,000 active duty troops and 2,000 National Guard personnel deployed in support of border security.
On Monday, Shanahan approved deploying an additional 320 troops to the border, a contingent that will include military lawyers to help represent DHS in immigration courts, support personnel to help provide food and other humanitarian care to migrants, and drivers to help transport migrants in CBP custody from border patrol stations to CBP facilities.
Asked by a skeptical lawmaker why the Defense Department was performing these duties and not DHS, Shanahan replied, "The simple version is that I have a legal standing order from the commander-in-chief to deploy resources to support a national emergency."
David Norquist, who is performing the duties of the Deputy Secretary of Defense, confirmed that the Trump administration has asked Congress for an additional $377 million to support the border deployments.
During a separate congressional hearing, Rep. Mac Thornberry, the ranking Republican on the House Armed Services Committee, asked Pentagon officials why the administration was using troops instead of contractors for the border mission.
"The border patrol is completely overwhelmed. Reports this week are that military folks are going to be asked to do more tasks at the border than they have been doing before. My question to you is why can we not use contractors for these support activities that we are now asking the military to do?" Thornberry asked.
The Pentagon has also shifted $1 billion in defense funds toward building barriers on the southwest border.