A U.S. Customs and Border Protection agent patrols on the U.S. side of a razor-wire-covered border wall that separates Nogales, Mexico from Nogales, Ariz., March 2, 2019 (AP photo by Charlie Riedel).

There has been much to criticize about President Donald Trump’s handling of America’s national security, including his recent declaration of a national emergency on the southern border. But while that declaration might be misguided, Trump has been right about one thing: The United States has never developed an effective strategy for the actual security challenges south of the border. Since the United States became a global power in the 20th century, it has used a sequenced method for addressing emerging threats—first building an understanding of them, then developing a working consensus among security experts and political leaders, and then relying […]