Everybody thinks the media are biased against their side, and conservatives are particularly likely to believe it. They themselves would say "That's because it's true!", but the real reason is that the complaint of liberal bias is one that conservatives hear all the time from all of their media sources. That isn't to say there aren't some issues on which the conservative side doesn't get equally favorable coverage, because there may well be a few, just as there are issues on which liberals get the short end of the media stick. But on some you can make a case that there are legitimate reasons. For instance, I wouldn't be surprised if a systematic analysis revealed that coverage of the gay-marriage issue was friendlier to the pro side. That might be because one side is arguing for equality and the other side is arguing for discrimination, and portraying the two as equally morally valid is itself problematic (I know, conservatives would disagree).
Anyhow, if there's ever a topic about which coverage should be emphatically even-handed, it's an electoral campaign. You've got two sides trying to achieve the same objective, both of whom represent large portions of the public. Aha, conservatives would say—but coverage of elections is totally biased against Republicans! And when you ask them to support this claim, their evidence usually comes in two forms. One is, "Here's an example of a story that was totally mean to our candidate!"—in other words, an anecdote. The other is, "If you can't see it, then you're hopeless." Which of course is no evidence at all.
But what happens when you actually try to analyze news coverage of campaigns in a systematic way? The results usually look like these, which come from John Sides and Lynn Vavreck's new book about the 2012 election, The Gamble:
You can see predictable spikes in the volume of coverage (the gray line) around big events. You can also see that Romney received somewhat more coverage than Obama in the outlets that General Sentiment was monitoring. But most importantly, you can see that once we factored in the tone of the coverage — the black line — the media favored neither candidate consistently. Sure, the week after the release of the 47 percent video was a rough one for Romney. But September wasn’t that great for Obama, either. Similarly, coverage of Obama was more negative, and coverage of Romney more positive, after the first debate — as the Project for Excellence in Journalism also showed using a different methodology — but this didn’t last long.
Ultimately, when we looked at the average across the entire fall campaign (and the same was true in the summer), we found that the tone of the coverage of the two candidates was almost exactly the same. Neither was covered much more positively or negatively than the other. This is consistent with the Project for Excellence in Journalism’s research and with scholarly research on previous presidential elections. Taken together, this is comforting evidence that the media writ large can approach election campaigns with minimal partisan or ideological bias.
Actually, this is a bit of a surprise. Most of campaign coverage is driven not just by the trivial ephemera of the moment (as in, "My opponent said something that, when taken out of context, sounds silly!") but by the ups and downs of the polls. When a candidate is leading or trending upward, he gets better coverage, since the journalists spend a bunch of time talking about how he's winning and all the things he's doing right. When a candidate is trailing or falling, the coverage is a mirror image of that. That coverage has a valence, but not a bias, or at least not an ideological bias. Since Barack Obama was leading in the polls pretty much the whole campaign, you'd expect that he would have gotten more favorable coverage, of the "Obama Leads, Romney Trails" variety if nothing else. But apparently not.
They don't say in this post (I assume it's in the book, which I haven't read) exactly how news stories were coded to determine how positive they were to each candidate, but the way those kinds of quantitative analyses of media coverage usually work is that you sacrifice some measure of subtlety in favor of greater objectivity. There may be complex ways in which the coverage favored Obama that only a particularly insightful semiotician doing a deep reading of each story could tease out. But on the broad measure of good stories and bad stories, it looks like the press didn't favor either candidate, which is what has been found the vast majority of times researchers have asked the question. Something to keep in mind the next time you hear someone say that the press is all in Obama's pocket.