The candidate has called Republican delegate rules "unfair" It’s no secret that Donald Trump loves a good lawsuit. Over the years, he’s sued former business partners, a journalist, and at least one little old lady—and on Sunday he promised to bring that litigious spirit to the 2016 presidential race. Facing an organized effort by rival candidates to game state selection rules and undermine his delegate haul, the Republican front-runner is threatening to sue for votes ahead of a potentially contested convention, a move that could foreshadow a new phase in the GOP’s ugly primary fight. “Just to show you how...