(CNN) – The McCain campaign has called him "The One" - but Sen. Barack Obama, the presumptive Democratic nominee, is no longer #1 on Facebook, a popular social networking Web site.
On the same day that Obama revealed his choice of Sen. Joe Biden as his running mate, Olympic darling Michael Phelps passed Obama in the number of "fans" or "supporters" associated with their respective pages on the site.
As of Sunday afternoon, Obama had roughly 1,383,000 "supporters" while Phelps, age 23, had more than 1,399,000 "fans."
Phelps' meteoric rise on Facebook was helped along by a congratulatory message many users saw when they logged into the site after the Baltimore swimmer captured 8 gold medals during the Beijing Games. The message contained a link to his Facebook page, where users could sign up as fans.
The Obama campaign's use of Facebook and other Web 2.0 and social networking technologies has been credited with building his base of supporters online - particularly those in the same age group as Phelps.
Though Obama now lags behind Phelps in terms of support on Facebook, the presumptive Democratic nominee is still far ahead of rival Sen. John McCain, the presumptive Republican nominee. McCain currently has roughly 215,000 supporters on the popular social networking site.
Phelps did not respond to CNN's request for comment about overtaking Sen. Obama on Facebook.