TPM Reader NR chimes in ...

So when Joe Lieberman is being primaried and there is a real chance he will lose, common wisdom says it is because the liberals are demanding ideological purity. But when Cynthia McKinney is being primaried and there is a reach chance she will lose, common wisdom is nonexistent.

Just 'cause the talking heads like Lieberman and don't like McKinney doesn't change the fact that grassroots, rank and file voters are using the primary process to select the candidates they like the best. That's the way it is, and the way it should be.

Sounds about right to me.