That's a good point, the response to which is that the Left, for some reason, does not harp on Rush's comments the same way that the Right constantly takes shots at Michael Moore.
Imagine a world where every day, a Democratic talking head repeated some outrageous comment of Rush's, commenting how this shows what whackjobs the right wing really is. Imagine a left-wing blogosphere jumping all over that comment, taking their own shots at Rush. You can bet that moderate Republicans would be taking great pains to distance themselves from Rush and point out that he is just a talk radio host.
In fact, arguably, the reason this scenario never happens is that Rush and Bill Frist are already so separate in the public mind that nobody even bothers to try and ascribe an identity of interests to them.
If this is false, then why the heck aren't we pursuing this Michael Moore strategy with outrageous commentators like Rush and Ann Coulter?
And if this is true, then are the centrist Dems REALLY doing such a stupid thing by distancing the mainstream of the party from polarizing figures on the far left?