Then why is he talking calling out the military and using them in this effort to deport?

Because money. Money and time.

If you want to deport 1.5 million people in the next few years, and end "catch and release" for hundreds of thousands more, you need detention facilities. Lots and lots of detention facilities.

Problem is, though, that it costs money and time to build and staff new detention facilities. By the time you buy the land, bid the construction contract, go through permitting, then actually build the thing, as well as hire and train all the staff....well, that doesn't happen in months. That's more than a year, closer to two at best - at least for the facilities that don't get bogged down in lawsuits and NEPA challenges and what have you. And Trump's only got four years.

But the military....ah, the military is just sitting there! All that land and buildings and personnel. And the budget! Boy, that's just the biggest budget in the whole budget. If there's anywhere we can just "find" the tens of billions of dollars worth of facilities and money we need to conduct this mass deportation, it's in the military. They'll never miss it - we just move some dollars around because of the emergency, and we're good to go.