An open seat in Colorado’s 5th Congressional District has led to open warfare within the state Republican Party. On one side of the GOP primary is Dave Williams, who was elected state party chair last year and now running for Congress. He claims the mantle of the bare-knuckle conservative fighter — and, in doing so, is leveraging the party’s resources to sling invectives at his opponent. On the other is his rival, Jeff Crank, a longtime radio host and vice president with the influential conservative advocacy group Americans for Prosperity, with a comparatively simple pitch: Let’s push the Republican cause forward, without turning the party against itself. Both men have run for the seat before, and both lost to retiring U.S.