Active-duty U.S. troops are now stationed inside the Border Patrol's holding facility in Donna, Texas, and monitoring migrant adults and children from just a few feet away, according to two current and two former defense officials, a move a congressman says comes close to violating a 140-year-old federal law.

An unprecedented number of families have been coming to the southern border over the past year, straining government resources and resulting in dangerously overcrowded detention facilities. From October through the end of June, the Border Patrol apprehended more than 688,000 people