The jockeying among the titans of the Supreme Court bar for a place at the lectern when the justices hear the next same-sex marriage case is as understated as it is unmistakable. In a half-dozen briefs filed in recent weeks, some of the best lawyers in the nation spent many pages arguing that their case was the right one in which to establish a nationwide right to same-sex marriage. They pointed out the attractive features of their own cases and the shortcomings of others. In legal jargon, streamlined cases without procedural pitfalls are said to be good vehicles. That made...