I had been searching for the right words to express why I didn’t think President Trump should give an interview to special counsel Robert S. Mueller III, but Chris Christie found them. On ABC’s “This Week,” the former New Jersey governor said Trump “should never walk into that room with Robert Mueller.” If he does, Christie suggested, the president’s affinity for the “hyperbolic” could set in, and when dealing with federal agents, “that can send you to jail.” There you have it: an interview could lead to jail. A Trump interview with Mueller would introduce a new variable at a...