As Chris Farrell said on Lou Dobbs...A one sentence order to the military, “Secure the southern border immediately”
That is precisely the correct response to the invasion, but...
Taking such an action just weeks away from the midterm elections would galvanize the Democrat voter base like nobody's business. It would quite literally create a blue wave, where currently none exists.
Much as I'd love to see a military response, Trump needs to stay his hand just an eensy bit longer.