Look, Harris is not stopping other Republican candidates from running. The fact remains that no other Republican wanted to run in the race because they knew that Harris was running. This is sour grapes on the GOP establishment. Their boy Jeb doesn't want the seat, so now they're discouraged and is undermining Harris with a pathetic whisper campaign (Republican "officials" making comments to FL newsrags, etc).
But the RNC will go all out to defend RINOs such as Chafee and Specter. Go figure.