As a key witness testified inside the Manhattan criminal courthouse on Tuesday morning, an increasingly familiar scene unfolded outside, as another in a parade of well-known visitors — this time Mike Johnson, the speaker of the House — stepped up to a microphone. “This is a man who is clearly on a mission for personal revenge,” Mr. Johnson said, attacking the witness on the stand, Michael D. Cohen, the former fixer to Donald J. Trump. “He is someone who has a history of perjury. No one...