GREENBELT, Md. —A federal grand jury is investigating the handling of the Justice Department’s criminal investigation into Democratic Sen. Adam Schiff , according to a law enforcement source and a subpoena to a witness requesting information about her communications with individuals purporting to be involved in the probe. The subpoena obtained by NBC News was sent to conservative activist Christine Bish, who testified before the grand jury on Thursday. It asked for any records Bish has from