Early Friday morning, President Trump tweeted, “Iran is playing with fire — they don’t appreciate how ‘kind’ President Obama was to them. Not me!” Earlier in the week, both the president and National Security Advisor Mike Flynn said they were putting Iran “on notice,” without defining what that notice meant. Mr. Trump likes to keep our adversaries guessing, and that’s a good thing, if he actually does it. More definitively, a statement by Flynn said, “The days of turning a blind eye to Iran’s hostile and belligerent actions toward the United States and the world community are over.” For the...