President Donald Trump has ordered 5,200 troops to the U.S.-Mexico border to repel what he calls an invasion. But the ongoing rush of Central American migration is significantly smaller than earlier surges. And like the previous wave of migration from Mexico, its probably not going to last. There simply arent enough people in Central America.

Theres just not much demographic potential for mass migration from Central America, said Douglas Massey, who has spent the last three decades tracking migration as a co-founder of the Mexico Migration Project . It is heading in the same direction as Mexico toward an aging population with limited growth, only the base population is much smaller.