Among the 11 public officials arrested in an F.B.I. corruption sting in New Jersey today was a leading Democratic supporter of Senator Hillary Rodham Clinton’s presidential campaign in that state, Mayor Samuel Rivera of Passaic. It was the latest legal embarrassment involving an ally of the Clinton campaign, coming only one day after a wealthy Clinton donor, Norman Hsu, missed his court date in a California fraud case and apparently disappeared. Clinton advisers this spring and summer have been aggressively touting their long list of endorsements from elected officials and prominent Democratic donors, to indicate the breadth of establishment support...