Well, once he has the troops at the border and the caravan turns back, he can use them to start building the rest of the wall.
What would be a great result from this military presence would be a big hit on cartel drug trade across the border. After all the videos from trail cameras showing cartel gunmen armed with AKs freely escorting large groups of their drug mules, a reduction of that activity would be nice. The cartel boys that lop off heads of competition may not end up being too happy with caravan heads after they bite into profits. We'll see after they get far enough North into cartel territory with their caravans.