The Democratic establishment dealt a crushing blow to the progressive movement Tuesday, when Shontel Brown, the preferred candidate of party stalwarts, triumphed over Nina Turner, a face of the insurgent left, in a special congressional primary election. Turner conceded shortly after 10 p.m. with a biblical reference: “On this night, we will not cross the river.” She trailed Brown 51 percent to 44 percent when The Associated Press called the race.