Yet another Republican is involved in scandal and CNN tries to make it sound like scandal plagues both major US political parties. TPM has a video clip documenting just how egregiously CNN doctors the "scandal balance."
CNN like Fox News, consistently exhibits a pro-Republican, pro-Bush bias. On CNN, the bias is not so explicit, but pertains to how headlines are written and stories structured.
The most likely explanation for CNN's bias is that Time Warner, the owner of CNN, has significant business interests that Republican politicians are far more likely to support. The same goes for Fox News, which is owned by Rupert Murdoch's Media Corp. Only the tactics differ. Both news networks could be viewed as corporate propaganda machines: their primary purpose is to serve the business interests of the parent company.