One big thing that has changed politics fundamentally is the extreme polarisation of the parties.(...) In 2010 Congress was more deeply split on partisan lines than at any time since the second world war, according to Congressional Quarterly(...). So far this year, a record 80% of roll-call votes in the House have pitted a majority of Republicans against a majority of Democrats. On average, House Republicans have voted with their party’s majority 91% of the time and Democrats 90% of the time. The picture is very similar in the Senate.
And now, for the list of possible reasons, let me put them in bullet-points form, the only form that matters. The reasons come from Dan Glickman, a former Democratic Representative and agriculture secretary, and Bob Bennett, a former senator from Utah
- Congressmen depend on money and are indebted to lobbies
- "The self-reinforcing partisanship of the media"
- The workload has increased and politicians are spending less time on the Hill, so that they have fewer interactions with the other congressmen. Related, the rise of television made congressmen talk to the camera instead of other congressmen
- They are less willing to show leadership because of division within their parties(e.g. Republicans who do not want to mess with the Tea Party)
- Primaries create incentives for moderates to appeal to more extreme members of their party. Think of Mitt Romney. In France, you can see the issue strongly for next year: Strauss Kahn is the strongest candidate for the Socialist party, but it is definitely not clear that he would win a primary against more leftist members(and this is what happened 4 years ago)
Those reasons are not all satisfying if we look at the graphs I posted earlier and if we want to understand what happened under Reagan. Note that the TV stuff is mentioned. One thing I like is the impact of the primaries, because if we think of the feedback loop I mentioned between party polarization and population's partisanship, the primary story could be the exogenous factor starting it: you have a primary, so candidates need to be more polarized. However, once again, this is not something that happened just at the start of the Reagan era.