Guests stand after a Rand Paul speech at the Conservative Political Action Conference (CPAC) in Rosemont, Ill. Conservatives celebrated Tuesday's victory in Wisconsin's recall election.
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Future U.S. senator and presidential candidate John Kerry poses with crewmates during the Vietnam War in this file photo. An attack on his service by a group calling itself the Swift Boat Veterans for Truth is remembered as a turning point in the 2004 election. But political scientists say negative ads might not be that effective.