The problem with the Senate is not that you can’t get 60 people out of 100 people to agree on something. It’s that roughly half the folks will lose any chance at a promotion, and they may even lose their job, if they agree with the other half. Bipartisanship isn’t impossible because people disagree on the finer points of American policy, though many of them certainly do. It’s impossible because the parties are locked in a zero-sum struggle for control, and you don’t gain an advantage if you give the other side a major accomplishment and then tell the American people they really did a good job reaching out to your and your colleagues. That’s the equivalent of saying to your employer, “Don’t give me a promotion, and in fact, think hard about whether you might want to lay me off next year.”
As I’ve said before, it is very near to impossible to build out an ideological model explaining why Republicans who voted for the deficit-financed Medicare Prescription Drug Benefit would vote against the deficit-neutral health-care reform bill. But it’s very easy to build out a model explaining why Republicans would vote for a bill that would help them if it passed and against a bill that would hurt them if it failed. Same goes for Democrats. Good-faith disagreement is not the explanation that best fits the data.