(CNN) -- How could they not have known they were asking for trouble? In the past few years, Rep. Mark Souder of Indiana had an affair with the staff member who had helped him produce a video promoting sexual abstinence. South Carolina Gov. Mark Sanford flew to Argentina for an extramarital tryst, instructing his staff to tell the press he was hiking the Appalachian Trail. Sen. John Edwards tried to pass off the daughter he fathered as the love child of one of his aides.