Here's another one that doesn't directly address the issue, but poses the question of how a liberally-biased media would be able to sustain itself.

And here is an article about liberals criticizing other liberals.

And here (ID9K) is an article stating how the current operating definition these days of a 'liberal' seems to be 'anyone who criticizes a conservative, no matter how much they may also criticize liberals.' That is, you get kicked out of the conservative camp for saying anything bad about conservatives anyway. By that metric, which may not necessarily be very accurate, but still seems to be in use, then of course more liberals criticize liberals than conservatives criticize conservatives, because a lot of the former used to be the latter, and still hold the same ideological views.

I'll also refer you to the Clipper chip controversy, when both liberals and conservatives ganged up on Clinton over the threat to privacy that a government-mandated standard for encryption technology (complete with backdoor provisions for government wiretapping) posed to the public, who would be forced to use the technology. And the media certainly covered the bipartisan aspect of the opposition.

Or how about sexual orientation and military service? Conservatives lambasted Clinton for even bringing up the subject, and as a result he backed off from completely lifting the ban on homosexuals serving in the armed forces. Yet liberals also took him to task, because DADT(DHDP)* didn't go far enough. And the media covered both points of view in that case as well.

In fact -- hey, the Web dates back to within Clinton's first term. Go back and search through the archives that are available on archive.org and elsewhere, and see how often the media were willing to criticize Clinton's policies and even his non-political activities. I think I've given you enough of a place to start from to relieve myself of this onus of which you speak.

_{* Don't Ask, Don't Tell (Don't Harass, Don't Pursue)}