NPR reported on a liberal response to Rush Limbaugh. He is no threat yet since he's only on a handful of stations and none of them are in large population centers, but he actually beats Rush in some of those small radio markets.
NPR : All Things Considered for Saturday, February 28, 2004 has a piece "Talk Radio's New, Liberal Hope" From the first link, scroll down to Talk Radio's New, Liberal Hope or click the audio link on the second link.
The 'liberal' host is a guy named Ed Schultz, who they describe as a "former conservative". Of course, he's not exactly a Massachusetts liberal. He likes hunting and he doesn't like abortion. The piece did not include enough about his political views to really clarify whether I would classify him as a liberal or not. It does sound like he's somewhere to the left of Rush, but that's not saying much.
The piece did clarify one thing. Even Mr. Schultz doesn't buy the notion that there's some sort of conservative conspiracy to squelch liberal talk shows. He's pretty sure that it all boils down to market success, not politics, when stations decide who gets to host a show.

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