Dunford says the troops, which could number as many as 15,000 according to the administration, are merely there to support the Homeland Security operation, and aren't intended to carry out any missions on their own.

This mad been a major question in the repeated deployment of troops to the border, as the Posse Comitatus Act is intended to prevent using the military in a law enforcement role, and officials have been very vague on what the troops will actually do.

That's still a question, with President Trump emphasizing the installation of "beautiful" barbed wire at the border in recent days. If the National Guard deployments are any indication, the reality is that the troops probably won't be doing all that much.