It’s a pretty common gripe for those dissatisfied with the American politics to lament the “two party system”, the assumption being that if there were more political parties, there’d be less partisan gridlock. I’m not inclined to believe this.
For example, look at the upcoming battle between Rep. John Dingell (D-MI) and Rep. Henry Waxman (D-CA) for committee chairmanship of the House Energy and Commerce Committee. Dingell, from Michigan, has been a friend of the auto industry, and is thus disinclined to push sweeping climate change legislation inimical to the interests of his constituencies. Waxman, on the other hand, is not bound by the constraints of auto manufactures and would be inclined to push sweeping climate change legislation. In any event, this dispute would still exist regardless of whether or not Waxman and Dingell were both Democrats because Dingell would still be representing the interests of auto manufacturers and Democrats would still need Dingell’s vote from time to time.
On the Senate side, consider Joe Lieberman. Joe Lieberman votes with Democrats most of the time, he just happens to be a foreign policy lunatic. In a multipolar political system where Lieberman could run the Domestic Liberal/Foreign Policy Lunatic Party (DLFPLP), Lieberman’s vote would still be valuable to Democrats, and Democrats would still, at least to a certain extent, need to cater to Lieberman’s interests.
There are endless examples of this, and indeed, in multi-party political systems, legislatures can often be held captive by the extreme parties. Simply put, it doesn’t really matter how narrowly you choose to dice political interests. So long as interests are represented and majority coalitions need to be formed, there will always be a need for compromise.