The Senators are pretty ticked off at the ESRB for not being as censor vicious as the BBFC. But the ramifications of the Senators' attack on the ESRB go deeper than Manhunt 2, and may affect the video game industry in general if the ESRB is put under the "thorough review" that they are demanding.
Even worse, the Senators are calling for more extreme ratings on the Wii, due to the console's motion-sensitive controller. They argue that the Wiimote "permits children to act out each of the many graphic torture scenes and murders."
Of course, they don't acknowledge the fact that children shouldn't be playing Manhunt 2 at all, since the game was given a "Mature" rating by the ESRB, and one of the few ways they can even play the game is with parental permission. If children playing mature games is really their concern, perhaps the Senators should be putting parents under review, and not the ESRB. Those old enough to play violent games can differentiate between using waggle and using real weapons, making separate Wii ratings unnecessary.
At times like these, we really yearn for Stephen Colbert to make a political comeback.