It appears that they could even pass some fixes for the Senate bill and then pass the bill afterwards, and that they only need 51 votes to pass the fixes (not sure exactly how this works, but apparently it's something that can be done). I don't know what's keeping them from doing that. Maybe they just want to allow Brown to be seated first for propriety's sake. It doesn't really matter if they wait until after he's seated, because that won't change anything with regard to the Senate bill.