How are dominant news sources liberal when they were notoriously non-critical of the Bush administration's war efforts in Iraq and Afghanistan up until Iraq was in the midst of a civil war (Which the "liberal" media was so kind as to refer to it as "sectarian violence"). The New York Times and NPR even refused to use the word torture to describe water boarding - despite the fact that if you dug into their archives they certainly called it torture when it was done to Americans by the Japanese during WWII.

The only issues where I'd say the news media is genuinely more liberal than the average American is gun control, and I'd say that has more to do with the fact that just about every person in the news media lives and/or works in a major City where gun violence is a problem. Considering gun control hasn't been a major platform issue of the Democratic party since the mid 90's, and is of little interest to the modern progressive/liberal movement (they are far more concerned with social and economic matters), it's hardly fair to classify them as across-the-board liberals.