Senator John Kerry marked the impending departures of Olympia Snowe and Richard Lugar from the US Senate by lamenting the loss of their bipartisanship, but his defense of both Republicans belied a simple fact: by one index, they have been more partisan than Senator Scott Brown, the Massachusetts Republican Kerry hopes to see replaced in the Senate by Democrat Elizabeth Warren. According to a study of 2011 Senate votes, Brown voted with his party just 54 percent of the time.