What do you know? Time magazine ran a list of the Top Ten Editorial Cartoons of 2007, and the only American political figures coming in for lampooning were . . . conservatives.Four of the cartoons were not explicitly political [sex habits of the elderly, contaminated products from China, VA Tech shootings, Barry Bonds steroids scandal].
But of those that satirized political figures, all were Republicans or conservatives:

When New-York based "Today" went looking for a local sports reporter to defend Barry Bonds the morning after he set the career home run record, it didn't turn to the New York Post, whose headline this morning reads JUNK BONDS: ‘SULTAN OF SYRINGE'. Nor was it likely that the designated hitter would be someone from the Daily News, whose back page screams "King of Shame." Instead, "Today" looked to the New York Times, and in particular to sports writer William Rhoden [pictured here with Matt Lauer], to embrace Bonds.