Time was when a journalist dissembling about his own recorded words, for heaven's sake, would have fallen into disgrace and out of a job. At the provincial level, that's still true. I'd expect to be sacked for such egregious misbehavior, which, possessing a sense of honor, I'd never imitate.
For the national political press, those days ended during President Clinton's first term. Much of the "mainstream" media now operates by Hollywood rules: Stardom brings big money and freedom from accountability. So long, that is, as one can avoid offending the Soviet-style propaganda apparatus that's arisen on the Republican far right.
But no, "both sides" don't do it. Berated for years about "liberal bias," many otherwise sensible citizens don't understand that for better and worse, the Democrats have nobody like Andrew Breitbart or Glenn Beck.