Missile defense should be one of his highest priorities. One of Donald Trump’s most consistent, if relatively neglected, policy promises during the campaign was to build an “Iron Dome” for America. Trump included the proposal in the Republican platform — “A GREAT IRON DOME MISSILE DEFENSE SHIELD OVER OUR ENTIRE COUNTRY” — and he talked about the “greatest dome of them all” at rallies. The idea got some more attention this week when Trump’s national security adviser–...