Pivot and Attack
Regardless of how you feel about the BetrayUs ad the single worst way you can respond to it is to sign on to any faux outrage coming from the right. Even if you are equally outraged, expressing that outrage simply compounds any "mistake" you think was made on the part of MoveOn.
Bill Clinton shows how it is done.
Pivot and attack.
Is it really that hard? Or does Clinton just make it look easy?