The press was at the height of its power when the Monica story began and Drudge was its underbelly.
Come to think of it, the underbelly of Clinton & Co. has been on display all summer.
c.1600, from under + belly (n.). In figurative sense of "most vulnerable part" it is recorded from Churchill's 1942 speech. Sometimes used erroneously in sense of "seamy or sordid part" of anything.