Fort Lauderdale has toughened its stance in the long-running debate over whether to build a bridge or tunnel to get commuter trains across the New River, now saying a tunnel is the only option acceptable to the city. That’s the latest move in what some fear might turn into a stalemate between Fort Lauderdale and Broward County over the fate of mass transit in South Florida. The back and forth has some wondering whether either one will ever get built.