One of the Indiana University professors who recently found that almost four times as many journalists self-identify as Democrats than as Republicans doesn't believe that that imbalance causes biased reporting.
IU's Lars Willnat remarked to Salon magazine that "we don’t think that our findings reflect a ‘liberal media bias’...Journalists’ political preferences don’t usually translate into political bias in news coverage unless they are working for openly partisan news media. Their professional norms and values, as well as market pressures, prevent most of them from being biased politically.”
Salon's Jim Newell, whose Wednesday piece relayed the comments from Willnat, went on to contend that journalists typically are biased -- not in favor of liberalism or conservatism, but rather toward whatever they think will advance their careers (emphasis added):
What motivates political journalists in the so-called mainstream media — as in news organizations that seek neutrality and objectivity, for better or worse, as their mission — is very rarely a right- or left-wing agenda. It’s careerism. You know, impressing the boss and moving up the ranks!
This about squares with my very non-scientific experience interacting with political reporters at these organizations. I have no idea what most of their politics are, and they probably don’t either. They have no time for long-term ideological plotting. It is always comical when someone accuses, say, Politico or the Washington Post of having some sort of institutional left- or right-wing bias; more often than not, the people there are concerned with getting a “scooplet” 15 minutes before some other outlet gets it. While D.C.-based political reporters, at least, generally are in favor of some Democratic positions such as marriage equality or gay rights, they’re also strangely likely to believe that it’s imminently necessary to make cuts to Social Security and Medicare benefits. So if there’s any bias that does come through in neutral, objective political news coverage, it’s a skew toward issues of importance to elites.