O’Reilly worked for CBS and ABC. He still defends their “integrity” and “credibility”, even though he’ll acknowledge their bias. He defends them from conservatives. He’s Establishment through and through.
Even when he ever had to report something "negative" about Obama or Hillary, he would only go half way... then soften things up with something stupid like "Republicans do the same thing too" or "I can see their reason for doing...".
He was always careful not to offend people because he was always thinking ahead to getting the next ratings drawing interview with the person.