Clinton Fights to Keep Impeachment TabooAfter Spat, Campaigns Know to Expect Swift Reprisal for Any Hint of the Scandal By Anne E. Kornblut Washington Post Staff Writer Sunday, February 25, 2007 Sen. Hillary Rodham Clinton has a new commandment for the 2008 presidential field: Thou shalt not mention anything related to the impeachment of her husband. With a swift response to attacks from a former supporter last week, advisers to the New York Democrat offered a glimpse of their strategy for handling one of the most awkward chapters of her biography. They declared her husband's impeachment in 1998 -- or,...