Kerry: Bush Lets Groups Do 'Dirty Work' BOSTON - Sen. John Kerry accused President Bush on Thursday of relying on front groups to challenge his record of valor in Vietnam, asserting, "He wants them to do his dirty work."   Fighting back, Kerry said if Bush wants to "have a debate about our service in Vietnam, here is my answer: 'Bring it on.'" Bush served stateside in the Texas Air National Guard during the war...