The Trump administration argues that migrants stopped on the Mexican side of the southern border have not "arrived in the U.S." and therefore have no right to seek legal protection on American soil. Immigrant advocacy groups challenging the Trump policy insist that blocking asylum seekers is plainly against the law.

But the looming possibility of military action against Venezuela – across a wide spectrum of violent options – drags the White House into realms of foreign involvement it has always said it loathed.

President Donald Trump said Monday he would be willing to launch military strikes inside Mexico to combat drug trafficking, telling reporters in the Oval Office that such action is “OK with me” and “w...