Quite frankly, he may need to put a lot of pressure upon Mexico to do the dirty work here. If he sends the military in and massacres them all, it could severely affect his chances during the mid-terms as it will be considered a massive abuse of human rights. If he lets it through, multiple caravans and boats will follow; just ask the citizens of Italy, Germany or Sweden. Those refugees numbers can swell into the millions surprisingly quickly. Such numbers will severely affect the future demographic of the nation.