Patricia Fernández-Kelly is a professor of sociology at Princeton University, where she directs the Center for Migration and Development. The views expressed in this commentary are solely hers.

(CNN) According to President Donald Trump, the mightiest, richest country in the world is under a threat so huge and scary that it will require the deployment of military forces -- as many as 2,000 to 4.000, Trump said Thursday -- along its 2,000-mile southern border. The danger consists of a ragtag caravan formed by several hundred impoverished people, many of them children from tiny Central American nations. Yes, the time has come to protect America from marauding youngsters and their parents.

Patricia Fernandez-Kelly

That preposterous notion would be the staple of satire were it not being proposed as a matter of policy by the leader of the free world.

Yet again we must ask -- does Trump have no shame? Is there no end to his malignant opportunism?

There is no immigrant invasion. There's not an avalanche of interlopers trying to break American gates in search of DACA relief. There is no reason to erect a wall or militarize the border outside the delusional world that the Trump administration has created.

Delusion, however, does not mean unreason. Trump's vocabulary of motives is of the most abhorrent kind--to preserve the support of people whose bigotry and fear are as great as their ignorance. By playing to the anxieties of his base, the President aims to bolster his popularity. His goal is to build American unity at the expense of desperate people displaced by terror and lack of opportunity in places like Honduras, Guatemala and El Salvador. Nothing in politics works better than to create fear of an external threat to rally internal support.