Fun wonkitudinal chartification of the day (original source: is.R()): The DW-Nominate scores of every single Congress since the founding of our union, charted by party.
In short, DW-Nominate (not 'Dominate,' as this blog post erroneously calls
it) is a scoring method that looks at the voting records of legislators and ranks them on a liberal-conservative scale. The scoring method is designed be consistent over time, so that different legislators in different periods can theoretically be compared to one another.
Specifically, notice the hockey stick shaped turn in the red line at the 94th Congress (1975), whereas the blue line has not really budged since then.
What does this mean?
It means that the Republican party has sprinted very far to the right since that time, while the Democratic party has remained just a step or two to the left of center. In other words, the Democrats have not turned into raging 'socialists,' despite what Fox News might tell you. But the Republicans have become a party that governs from the far right, yet somehow has managed to carry about half of the American electorate along with them (most likely unbeknownst to some of those voters, whose party identification is stable, even if their party's ideology is not).
As far as I am aware, DW-Nominate is about as non-controversial a measurement technique as there is (i.e. it has not been accused of having some sort of pernicious liberal bias). And it can be used to tell us lots of other interesting things: for example, that Paul Ryan is the most extremist VP pick for either party (highest or lowest DW-Nominate score) since at least 1900.