Keillor is lifelong Democrat and host of the downhomey Prairie Home Companion radio show. His comments after the last election have caught some flak recently. Here is a GetReligion post. The Volokh Conspiracy is commenting here and here. Instapundit as well.
Suffice it to say that Keillor probably shouldn't have make jokes about disenfranchising evangelical Christians. Eugene Volokh (not christian last time I checked) found the joke distasteful because "I suspect that much of Keillor's audience does dislike born-again Christians, and that a considerable chunk even holds them in contempt."
The problem with this is that Keillor actually has a significant evangelical audience. My parents used to listen to him regularly. He plays old timey gospel music. He does a lot of clean humor. Much of his act is like a small town observational comedy. He is pretty big in the Red states who want something that speaks to them, but doesn't border on the profane as much as, say, the Blue Collar Comedy Tour. Do you honestly think the urbanites of New England listen to a show called Prairie Home Companion?
So hopefully for Keillor, those christians did think it was funny because if they didn't he's lost a big market segment for his show.