Justice Department officials in Washington have issued a rare threat to sue Maricopa County Sheriff Joe Arpaio if he does not cooperate with their investigation of whether he discriminates against Hispanics. The civil rights inquiry is one of two that target the man who calls himself "America's toughest sheriff." A federal grand jury in Phoenix is examining whether Arpaio has used his power to investigate and intimidate political opponents and whether his office misappropriated government money, sources said.R@L ....