Sen. Arlen Specter is always near the bottom of those lists of the most partisan members of the Senate. Through his 28-year career as a Republican senator, he repeatedly bucked his party's wishes to side with Democrats. The Washington Post's vote-by-vote list of Specter's defections goes on for 16 pages—and it only goes back to 1991.
The traditional way to measure unorthodoxy is by counting the number of times a senator voted against a majority of his or her party. (Congressional Quarterly, the authority on vote studies, counts only votes in which a majority of Republicans opposed a majority of Democrats.) By CQ's rating, in only one year of the last 28—2003—did Specter vote with Republican senators more than 70 percent of the time.
But there are other ways besides statistics to demonstrate the degree to which Specter was an outcast from his party before he defected. To draw that picture, Slate presents the Senate as a Facebook-style social network. Here's how it works:
- Red dots are Republican senators, blue dots are Democrats, and Specter is purple. The two independents, who caucus with Democrats, are light blue.
- Any two senators are connected if they have voted the same way on 65 percent of the votes in 2009—an admittedly handpicked threshold number that best displays the connections and divisions.
- Mouse over a dot to see a senator's name. All those to whom he is connected—that is, those he has voted with at least 65 percent of the time—will be highlighted in yellow.
- There are nearly 2,400 connections among the senators, so at first the graphic will look chaotic and bounce around a bit. Eventually, like the Senate itself, it will resolve to an equilibrium that shows two distinct camps.
As the graphic shows, Specter is connected to only 14 Republicans, while most Republicans are connected to every other. Democrats are also very insular: With the exception of Ben Nelson of Nebraska, most vote along party lines.
Perhaps more surprising is that Specter is (rather, was) not even the most renegade member of the GOP. That title would be shared by the two Republican senators from Maine: Olympia Snowe and Susan Collins. This so-called Gang of Three is familiar to anyone who follows the divided Senate.
Whatever the effects of Specter's defection, one can certainly say this of the Senate in the supposed age of postpartisanship: Of the 99 senators, 95 remain safely ensconced in their parties, huddling together for warmth.