David Broder writes today, “It’s been more than four decades since Arlen Specter, senator from Pennsylvania, earned the nickname ‘Specter the Defector.’ With his decision this week to leave the Republican Party, he confirmed that it is indeed an accurate description of his political character…But much as Specter’s decision reflects an increasingly serious weakness in the Republican Party, there is no escaping the fact that it is also an opportunistic move by one of the most opportunistic politicians of modern times. The one consistency in the history of Arlen Specter has been his willingness to do whatever will best protect and advance the career of Arlen Specter.”

Broder was much more understanding when Joe Lieberman became an “independent” after losing his Democratic primary race against Ned Lamont in 2006. Senate Majority Leader Harry Reid “will have to contend with a few real mavericks and independent spirits in his caucus,” Broder wrote in November of that year. “Sen. Joe Lieberman of Connecticut…has reiterated his intention to follow his own path rather than accept party discipline. He has staked out a position on Iraq – opposing any timetable for withdrawal – that is at odds with the prevailing inclination of the new majority.”

Personally, I think Specter and Lieberman are both flagrant opportunists, but it’s hard to understand why Broder is so indulgent of the latter and so critical of the former. Actually, given Broder’s right-of-center politics, maybe it’s not.