WASHINGTON (AP) - A comment by retired Gen. Wesley Clark that seemed to chide fellow Democratic presidential candidate Howard Dean for skiing as Clark recovered from Vietnam War wounds amounted to nothing more than an attempt at humor that fell flat, Clark said Sunday. ``Politics is easy, but humor is tough,'' Clark said.Clark ended a 34-year Army career in June 2000, shortly after completing a tour as NATO's supreme allied commander in Europe. As a 25-year-old commander of a mechanized infantry company in Vietnam, he was awarded the Silver Star for gallantry and the Purple Heart after being shot four...