Tacoma News Tribune columnist Peter Callaghan has an excellent piece out about the impacts of multiples candidacies and the top-two primary election. Among other things, it makes the clear point that the sheer number of (substantial) candidates who run can make a lot of difference.
He cites the 1996 governor's race, and the primaries in it. In that case, six substantial Republican candidates fought it out, with the plurality win going to Ellen Craswell, a Christian conservative state legislator who had enthusastic support which was limited to a relatively narrow ideological band. The Democrats had three major candidates, the winner being King County Executive Gary Locke, who had a broader base of support. Locke crushed Craswell in the fall.
But that wasn't the only point. Callaghan: "Republicans so divided the primary vote that even though Craswell got the nomination, she finished third behind both Locke and Rice. If the current top-two primary had been in place, no Republican would have made the general election."
Even long in advance, Republicans ever since have been trying to rally, early on, around one major candidate (like a Dino Rossi in three major elections, and now Rob McKenna for governor) to avoid that problem. And yet that hasn't been working out so well either.