The notion of a liberal bias in the mainstream media is decades old. From my recollection, I think it started in the Nixon Administration, when conservatives, possibly frustrated by the ethical lapses of their party's nominee and President, went looking for a boogeyman to blame. I have always contended that it really doesn't exist, that the center-left orientation of the mainstream media reflected the general consensus of the population at large, or at least, the portion of the population following the media news. The only real bias of the media is a ratings bias; that which generates good ratings is what gets covered.
But that was before the advent of the Internet and cable television, when it became possible to carve out specific demographics of the media-consuming public, and make a big business out of specific political orientation. Thus sprang to life things like right wing radio, and it's become a huge business. Of course, the political slant of narrowly-focused media doesn't represent mainstream thought; it's not supposed to. If someone like Rush Limbaugh can capture 90% of a market which represents 30% of the political thought in the country, it's a whopping demographic in media terms, resulting in many millions of dollars of revenue.
Right wing media has a problem, though; it can't be perceived as too blatantly biased, or else it can't achieve much growth. Therefore, we have Fox News, and its' 'Fair and Balanced' slogan. It's not hard to find a conservative fan of Fox News who thinks that the slogan is actually true, but it's even harder to find even a centrist who thinks it is.
I ran across a posting this morning on http://www.washingtonmonthly.com/ which illustrates the point. Fox News is fond of running 'polls' on political issues. These polls are just as meaningless on Fox News as they are on MSNBC, of course... they're not even remotely scientific, and reflect just the opinions of viewers, who, by the very nature of the media, are biased to begin with. The thing I found so incredibly interesting, though, was just how blatantly biased the questions can be. Here are some examples:
* "Do you think former President Bill Clinton's meeting with North Korean dictator Kim Jong-il and securing the release of the two American journalists will encourage kidnapping of more Americans or not?" (Fox News poll, August 2009)
* "Barack Obama says he quit smoking cigarettes. Do you think Obama is still sneaking cigarettes at the White House or do you think he has completely quit smoking? (Fox News poll, June 2009)
* "Do you think the United Nations should be in charge of the worldwide effort to combat climate change and the United States should report to the United Nations on this effort, or should it be up to individual countries and the United States would be allowed to make decisions on its own?" (Fox News poll, April 2009)
* "How much do you think Barack Obama loves America?" (Fox News poll, June 2008)
* "Do you think illegal immigrants from Mexico should be given special treatment and allowed to jump in front of immigrants from other countries that want to come to the United States legally, or not?" (Fox News poll, April 2007)
* "Do you think the Democratic Party should allow a grassroots organization like Moveon.org to take it over or should it resist this type of takeover?" (Fox News poll, March 2007)
Amazing, isn't it?