Are you certain it's 80%?
According to Bernard Goldberg's book BIAS, and the many polls and statistics he cites, yes.
well if it's in a bernard goldberg book called "Bias" then it must be true.

Though you've proven yourself to be someone who has their own unique view on reality that is grounded in your own bias and hatred so what does it matter? you hate the media because you don't like the stories they put out there and you ignore every other story that proves you wrong. it's easy to say the media is bias when you have your mind made up about everything in the world the moment you wake up in the morning.
praise allah for fox news.
Dumbass:
First, you haven't read the book, so you're talking out your ass, with no actual knowledge of what you're talking about.
Second, Bernard Goldberg didn't make up these statistics, he just quoted them from well-known polling services, who tabulate using scientific methods. The one that caught my attention most was that reporters THEMSELVES categorize their views as "very liberal". And that 10 of 10 white house correspondents said they voted for Mondale and 0 voted for Reagan (10 of 10!).
Gee, I wonder how that might have affected coverage of the 1984 campaign.
We certainly saw that trend in the knife-jabs the media took at McCain, as contrasted with the endless fellating of Obama.
Where the media had clear evidence of Obama's marxist/radical-socialist past (ACORN, William Ayers, Jeremiah Wright, Valerie Jarrett, Van Jones, Mark Lloyd, teaching Saul Alinsky to activists in Chicago, Cloward and Piven Strategy, Obama's own mother and father's marxism...) they simply ignored it and chose not to report it. While every half-baked rumor of a scandal about McCain got maximumn coverage, and on several occasions the lack of evidence and the visible double-standard blew up in their faces.
Similarly in November 2004 the Dan Rather scandal on the fake letter alleged to be from Bush's national Guard commander, proven fake, NOT by the media, but by bloggers more responsible than the media.
Similarly in 2006 the Mark Foley scandal, which was proven the liberal media knew about for a year, and unveiled as an October Surprise on the Republicans (with lots of false smear to Republicans way beyond Foley)
Both of these elections were hit jobs with the media and Democrats working in concert for victory.
The polls of reporters show similarly skewed numbers of overwhelming support for Democrat presidential candidates, way above the ratio of American voters who supported Democrats.
Similarly media coverage of the Bush/Gore and Bush/Kerry races. But never was the media working more as an extension of the Democrat party than in the 2008 election.
So far.
All of which is more quantifiably true than you talking out your ass about things you clearly don't understand.