Cops, when observing a mugger pointing a gun at someone, don’t wait for the trigger to be pulled before taking the mugger down.
Likewise, methinks the investigators should not wait for the actual corruption of a Senate appointment before moving. Intent was made absolutely clear - shut it down now before any more damage is done.
I see your point, but this is not a ‘violent’ crime and Blago was not ‘pointing a gun’ at anyone’s head. Fitz could have ensnared others. Either he knew the press had already blown his wiretaps to the players or he was protecting someone or something.