Seems that the assumption here is that republican leadership knew of the sexual tone in the IMs, so far, they've said they only knew of the email Foley sent requesting a picture.
The GOP leadership may be blameful or blameless in 20/20 hindsight, but the details are not going to matter. They are going to be blamed and tarred repeatedly over the next weeks regardless.
What matters is that when it became obvious to them, they took immediate action to end any association with him. Contrast that with the dems behavior re: Studds. They accepted him wholeheartedly.