It’s tough to find any semblance of a silver lining in the humiliating implosion of Donald Trump’s foreign policy over the last year, especially after a week that has brought us another escalation of the war no one supports, a recycled trade war with Canada, an out-of-nowhere nuclear deal with a country that should never have access to nuclear weapons, and yet more threats against a small nation that poses no threat to the United States. But here’s the upside, just maybe: The tiny and perverse cadre of “anti-anti-Trump leftists” has been decisively silenced. If you find that phrase baffling, consider...