In a joint study conducted by George Washington and New York universities, the 73-year old Republican was found to have the highest “Digital IQ” in the Senate, what the researchers are dubbing as the “definitive benchmark for online competence.”

The Digital IQ index combined senators’ use of social media websites like Twitter, Facebook and YouTube with the frequency with which members posted as well as their followings.

But it’s not just McCain, the 2008 Republican presidential nominee, who’s the GOP standard-bearer for social media. In a social media game mastered by the campaign of Barack Obama, the study found Republicans have “struck back,” with GOP senators averaging more than 5.5 IQ points higher than their Democratic counterparts.

Of the seven senators who scored “genius” social media rankings, four were Republicans: McCain — the top tweeter, Jim DeMint of South Carolina, Scott Brown of Massachusetts and John Cornyn of Texas.

DeMint is a tea party force, and Brown rode significant grass-roots tea party support to upset Martha Coakley for the late Sen. Ted Kennedy’s seat last winter. Cornyn is the head of the Senate GOP campaign organization.

“This study underscores the reality that social media is not a toy, and that digital literacy and agility are powerful tools in today’s business and political arenas,” said George Washington University School of Business Dean Doug Guthrie. “It appears that U.S. senators are making their comprehension of the social media realm a priority and are using it as a way to engage prospective voters and mobilize grass-roots efforts.”

Sen. Al Franken of Minnesota, the former comedian and radio talk show host, and Senate Majority Leader Harry Reid were the only Democratic senators to crack the top-five of the Digital IQ index rankings, tying for fourth with Cornyn. Sen. Barbara Boxer (D-Calif.) was the seventh “genius.”

In one of the more striking statistics, the study found that Republicans, a minority in the Senate, outpaced Democrats in terms of absolute online growth in July, accruing more than 3,000 more Twitter followers and 20,000 more Facebook “likes.” GOP senators have experienced a 6.7 percent month-to-month growth on Facebook, compared to 3.6 percent for Democrats.

These numbers exclude outlier McCain, whose prolific following tilts the findings significantly. The veteran senator, maligned on the presidential campaign trail at times for being out of touch, leads all members with 625,000 Facebook fans, nearly triple the total of second-place Brown and more than 8.5 times the number of third-place Sen. John Thune (R-S.D.).

Though Republicans are enjoying a clear social media advantage, the gap between the right and the left is smaller among the 27 members seeking reelection, with IQs only differing by three points.