My big takeaway:
"Most of the evidence suggests the trend is asymmetric: Republicans in Congress have become much more conservative, while Democrats have become only somewhat more liberal."
Sorry, couldn't resist that. But it does underscore my own superficial observations, and puts into question the usual Conservative assertion that they are holding the true center, as the founders envisioned it, while the Dems are all in a mad scramble to swing as unreasonably towards Socialism as possible.
Still, an excellent overall analysis, which underscores another one of ny superficial observations. Political science is to elections as lawyers are to justice, or as Marketing is to the Free Market. They are all attempts to spin the data and tilt the playing field and otherwise pervert the natural checks and balances in the system.
As per usual, convincing people they need to go into debt and pay too much for what they don't want and don't need seems to be attracting our best minds, and rewarding them disproportionately for their skill at lying.