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For those of my friends discussing our political system, here is a movie that uses data from every single roll call vote by every single Senator or Representative since the 1st Congress. Using social networking algorithms, they can orient everyone by the similarity of their votes. Then they can normalize it all between Congresses by using people who carry over from one congress to another.
This represents over 14,000,000 decisions by more than 12,000 people.
It is a fascinating movie but you can also see that most of the time, you can draw a straight vertical line between the two. Because most decisions are made along a single left-right economic axis. Actually pretty simple.
But watch around 1829-1951 as the question of slavery began to destroy the system. A second dimension appears, culminating in such chaos that even a 10-dimensional fit does not work.
When things are done, there are two parties again separated by a vertical line.
Another period 19 about 1940-1970, as Southern Democrats spilt along a second axis, moving up and to the right compared with the other Democrats. We are watching the effect of the Civil Rights era on the makeup of the political parties.
When this process is done, the parties again align in two groups separated by a vertical line.
Image: Allison Miller