Does NPR have a political bias?

NPR has held the distinction of being one of the least biased, most objective media outlets for many years, along with the BBC and PBS. Because of the firing of Juan Williams as a result of his statements on Fox News, NPR is now being accused by Fox News and members of the GOP as being a left-wing media outlet. As a point of comparison, several weeks ago a misconstrued message about NPR telling its employees they aren’t allowed to attend the Jon Stewart rally in DC led many people to claim NPR is a right-wing organization.

What do you think? If you think it has a left or right bias, please provide some evidence to support your decision.