U.S. President Donald Trump’s scaling-back of joint military exercises with South Korea is the latest impulsive and thoughtless decision in an accumulation of foreign policy insults that is leading to the U.S.’s abandonment of the world’s democratic community. These include Trump’s drastic cut in support for Ukraine in deference to Russian President Vladimir Putin and similar cutbacks in arms sales to Taiwan in deference to Communist Party Politburo Chair Xi Jinping, besides the inexplicable effort to assuage the feelings of terrorist dictator Kim Jong-un. These are coincidentally the countries with the three largest nuclear arsenals aimed at and capable of...