Sean Quinn at FiveThirtyEight.com:
[T]he Obama brand and Limbaugh brand are in direct opposition. Obama’s brand is about intellectual curiosity, empathy, personal respect for his ideological counterparts, and problem-solving. Limbaugh plays “Barack the Magic Negro” on his show and makes fun of Michael J. Fox’ Parkinson’s disease.
Prometheus Unbound 
You do realize that you’re playing into a false dichotomy here, right? The left wants nothing more than to make Limbaugh the modern voice of conservatism. That would be like the right saying that Al Sharpton is the leader of the liberal movement.
Andrew,
The difference between Sharpton and Limbaugh is this: Sharpton has very little power within the Democratic Party; Rush Limbaugh actually has quite a bit within the Republican Party. You’re right that liberals (like myself) are happy to call Rush Limbaugh the most popular, most enthusiastically followed Republican in the country. But it also happens to be true.
—Santi