At least two migrant children died in May at the U.S.-Mexico border, including a boy with the flu and a 10-month-old who drowned in the Rio Grande. President Trump is misguided in using tariffs against Mexico to solve the border mess, but he’s right about the crisis of families with children arriving to exploit U.S. asylum law. He’s also right that Democrats refuse to help.

The statistics tell a story of border mayhem, and these aren’t invented by White House aide Stephen Miller. In the first eight months of fiscal 2019,...