Is there a crisis on America’s southern border? Statistics out last week would seem to suggest so. According to U.S. Customs and Border Protection, more than 66,000 aliens were apprehended as they tried to sneak across the border last month, the highest February total since 2008 and the highest total in any month since 2009. Add in those deemed inadmissible at ports of entry, the total is more than 76,000.

The problem isn’t gaps in physical barriers, but in legal ones. Loopholes in U.S. immigration law, combined with a weak...