GOP critics cranked up the political heat Thursday on Attorney General Eric Holder, threatening impeachment and accusing him of withholding information from Congress about Operation Fast and Furious, a severely flawed and discredited federal gun-sting program. At the end of a long, combative day of testimony before the Republican-controlled House Judiciary Committee, California GOP Rep. Darrell Issa compared Holder to disgraced Nixon-era Attorney General John Mitchell. Holder shot back by comparing Issa to Sen. Joe McCarthy, the infamous Wisconsin Republican censured by the Senate in 1954 for leading what critics called a Communist witch hunt. "As they said in the...