The groom and groom strolled down the aisle to the mellow strains of “Mr. Sandman.” Wearing her black robe with her signature white lace collar, Justice Ruth Bader Ginsburg presided over the marriage on Sunday afternoon of Michael Kahn, the longtime artistic director of the Shakespeare Theater Company in Washington, and Charles Mitchem, who works at an architecture firm in New York. The gilded setting was elegant: Anderson House in the Embassy Row neighborhood, the headquarters in Washington of the Society of the Cincinnati, a club for the descendants of the French and American soldiers who fought in the Revolutionary...