President Barack Obama has received the most unrelentingly negative media coverage of any presidential candidate in the past five months, according to a Pew Research Center study released Monday.

The study, conducted by the Pew Project for Excellence in Journalism, would seem to crack the common image of a liberal mainstream media.

Researchers looked at coverage from more than 11,500 news sources: both print and online and both local and national. They found that only 9 percent of the coverage of Obama was positive, while 34 percent was negative.

The results for the Republican candidates were universally better. Rick Perry received the most positive coverage (32 percent), followed by Sarah Palin (although she never declared her candidacy) and Michele Bachmann with 31 percent each, and then Herman Cain with 28 percent. Mitt Romney came in fifth with 26 percent positive coverage.

Coming in behind Romney were Rick Santorum, Ron Paul, Jon Huntsman, Newt Gingrich and Tim Pawlenty, in that order. Even Pawlenty, who dropped out of the race in August, received more positive coverage than President Obama.

Trends among the Republican candidates have fluctuated with public opinion: for example, Cain has received increasingly positive coverage in recent weeks and Perry increasingly negative coverage. But the negative coverage of Obama has been a constant.

Though covered largely as president rather than a candidate, negative assessments of Obama have outweighed positive by a ratio of almost 4-1, the Pew researchers said in a press release accompanying the study. Those assessments of the president have also been substantially more negative than positive every one of the 23 weeks studied.

Interestingly, the two figures who have been arguably the most vocal critics of the mainstream media -- Rick Perry and Sarah Palin -- actually got the best coverage.

When Palin finally confirmed that she would not run for president, she said Obama had about 90 percent of the media still there in his back pocket. But the numbers from Pew don't back that up.

Tim Graham, Pew's director of analysis, said he did believe there was some bias toward Obama in the media. Obviously, we are in an atmosphere now where you can't be as gassy about how wonderful Obama is, because reality has intervened, he told Politico. But I think that there's still a notion that he's the sober and the serious one.

But the fact remains that, from May 2 through Oct. 9, there was not a single week in which more than 10 percent of the coverage of Obama was positive -- not even the week Osama bin Laden was killed. And among the Republican candidates, conservatives like Bachmann, Cain and Perry have gotten better coverage than the more establishment Romney.

The truth about the American media, columnist Jonathan Alter told Politico, is that we have gone, over the last 15 years, from something that could accurately be called a dominant liberal media -- through the period of American liberalism, from the end of World War II to the founding of Fox News in 1996 -- to a dominant conservative media in this country.