By ordering 800 National Guard troops to Washington, on the pretext of an illusory crime wave, President Trump has further dragged the U.S. military into domestic law enforcement, in a move credibly perceived as an ominous “test case.” This continues what the administration started in California in June as part of the its deportation efforts. Unfortunately, though we (and others) had hoped that the military would only respond to calls to action in American cities and states kicking and screaming, we no longer expect resistance from that institution. Once, perhaps, traditionalist officers might have leaned on protocol and refused to...