Congress is now grappling with a definition of a journalist as it debates a media shield law that would protect reporters against "unwarranted intrusion" by federal prosecutors, in the words of Sen. Chuck Schumer. The bill passed the Senate Judiciary Committee with bipartisan support earlier this month and could soon be headed to the Senate floor. It sprang to life after a spate of intrusions by the Justice Department last spring graphically demonstrated how overzealous law enforcement can threaten the vitality of independent journalism.In one case, the department subpoenaed the phone records of Associated Press personnel who had broken a story about a failed terrorist plot in Yemen.