A federal grand jury is convening to investigate former presidential candidate John Edwards in connection with possible campaign finance violations related to paying his mistress, Rielle Hunter, The ENQUIRER has learned exclusively. At least four former Edwards campaign workers recently received secret subpoenas to testify in Raleigh, N.C., according to a close source in Washington, D.C. One witness has confirmed receipt of the government document and has already contacted a lawyer, according to the source.