According to two defense official familiar with the request, the Department of Homeland Security asked that the Pentagon provide a reserve force that could be called upon to provide “crowd and traffic control” and safeguard Customs and Border Protection personnel at the border to counter a group of Central American migrants walking to the US border to request asylum.

The Pentagon rejected the request on October 26, according to one of the officials, even as it signed off on providing DHS with air and logistics support, medical personnel and engineers.

The request was turned down because the Department of Defense felt that active duty troops do not have the authority to conduct that type of mission unless they are granted additional authorities by the President.