The New York Times' political number cruncher, Nate Silver, has a very good column on why the political landscape looks the way it does. His explanation of why we now have more "safe" congressional districts than we once did seems very solid.
I find intriguing his analysis of why the GOP has an edge in the House whereas the Dems have one in the Senate. He predicts that the current split is likely to continue for several electoral cycles.
Silver doesn't emphasize enough the concern congressmen (and women) in safe districts feel about primary challenges by more extreme candidates of their own party. Sen. Dick Lugar (R-IN) is an example of a long-serving senator who was defeated in the Indiana GOP primary.
