a scatterplot timeline of the ebb-and-flow of party politics in the US Senate since the beginning of the modern (Democrat & Republican-dominated) 2-party era. the ideological measurements are based on the DW-NOMINATE algorithm, which take into account historical Senate Roll-Call votes.

the timeline conveys a sense of that shift by depicting the scaled left-right ideological positions of each Senator along the vertical axis. some of the patterns include the change in distance between the parties up until the mid-20th century, & a realignment in the late 1970s-early 1980s, where the polarization of the electorate & of elected officials became a dominant trend.

[link: duke.edu & princeton.edu & voteview.com & slate.com]