Trump goes to Yuma: Walls can work, but they can't work alone

In August 2016, Donald Trump made a memorable visit to Arizona. Then-candidate Trump had been rumored to be pivoting toward a softer immigration stance. But he put that rumor to rest when he addressed a rally in Phoenix.

Trump called once again for the building of "a great wall along the southern border," for which Mexico would pay. He additionally promised to end the "catch and release" policy for those apprehended while crossing and announced a "zero tolerance" policy for criminal aliens, of which he said there were at least 2 million in the United States. Finally, he promised to "block funding for sanctuary cities" that refuse to cooperate with immigration authorities in handing over criminal aliens for deportation.

Today, Trump has either made good or made progress on three of those four main promises. His efforts to deprive sanctuary jurisdictions of some funds have already caused some of them to drop the distinction, although others have promised to sue. Catch-and-release was abolished in April, and the immigration service has arrested and expelled about 84,000 charged and convicted criminals, fugitives, and repeat violators since Trump took office.

Among those removed: 2,700 gang members, more than 30 percent more than were removed in all of fiscal 2016.

But what about Trump's most conspicuous promise, which he has not fulfilled? Without having devoted more than a trifling sum to his "great wall," it appears that Trump's simple announcement of his intention to enforce existing immigration laws has all on its own sharply curbed illegal border crossings. During the first six full months of Trump's presidency (February through July), apprehensions at the southwest border are down 56 percent from the prior year.