National Journal announced on Thursday that Senator John McCain--the Arizona Republican and 2008 presidential nominee--had emerged from the publication's analysis of 2010 Senate votes as the chamber's most conservative member, sharing the title with seven colleagues.

McCain had hovered around the Senate's ideological center in National Journal's rankings earlier in the decade, when he earned a reputation as an independent-minded "maverick" by partnering with Democrats on contentious issues such as campaign finance reform and comprehensive immigration reform--a mystique that followed him through the 2008 presidential campaign. Fast-forward to 2010. How did McCain come to earn his most conservative score since entering the Senate? Here are the explanations on offer:

  • 2008 Election  Michael D. Shear at The New York Times explains that the presidential campaign forced McCain to become "the standard-bearer of the Republican party" and he seemed to relish the new role, ratcheting up the "anti-Democratic rhetoric" as the campaign wore on. Shear adds that this spirit of opposition persisted after Barack Obama become president and manifested itself, for example, in McCain's criticism of health care reform.
  • Republican Party Dynamics and Arizona Primary  National Journal's Reid Wilson notes that McCain's shift "is emblematic of the Republican Party's shift rightward" and also a product of his strong primary challenge in 2010 from J.D. Hayworth, who criticized McCain for not being sufficiently conservative. And indeed, the man who subtitled his 2003 memoir "The Education of an American Maverick" told Newsweek during the primary that "I never considered myself a maverick. I consider myself a person who serves the people of Arizona to the best of his abilities."
  • Legislative Agenda  A McCain spokeswoman tells National Journal that it's the legislative agenda in the Senate that's changed, not McCain's ideology.
  • Maybe He Didn't Move That Far Right  Hot Air's Ed Morrissey cites another study that analyzed all Senate votes (National Journal chose 96) and concluded that in the recently concluded 111th Congress, McCain was the 26th most conservative Senator.