Not to get political here. This is just an observation of the actually party breakdown in the Senate. The reality is that the republican party, particularly in the Senate, is divided. There are really three parties. The Democrats, the Republicans and a ReDemricans. That 3rd party being comprised of Collins, Romney, Murkowski, Sasse, Toomey and a few others whose names I can recall right now. McCain was among them.
With this three party system in the Senate, where each generally stays unified, the Republicans haven’t has anything more than a super slim majority when there were 40 dems and Scott Brown won his seat, giving the Republicans and a Redemricans a combined 60 seats. The problem was that 3rd party, the Redemricans usually voted with the Dems.