Republican presidential nominee Mitt Romney meets audience members after he addressed the U.S. Hispanic Chamber of Commerce in Los Angeles on Monday. Charles Dharapak/AP hide caption

itoggle caption Charles Dharapak/AP

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. Scott Olson/Getty Images hide caption

itoggle caption Scott Olson/Getty Images

Supporters of Texas Rep. Ron Paul cheer as the Republican presidential candidate speaks on March 28 at the University of Maryland in College Park, Md. T.J. Kirkpatrick/Getty Images hide caption

itoggle caption T.J. Kirkpatrick/Getty Images

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. AP hide caption

itoggle caption AP

A voting regulations sign is displayed at the Shandon Fire Station in Columbia, S.C., on Saturday. Win McNamee/Getty Images hide caption

itoggle caption Win McNamee/Getty Images

Joe Allbaugh, left, speaks to the press in Austin, Texas, in this Jan. 4, 2001, photo after being named as director of the Federal Emergency Management Agency by then President-elect George W. Bush.

J. SCOTT APPLEWHITE/ASSOCIATED PRESS hide caption

itoggle caption J. SCOTT APPLEWHITE/ASSOCIATED PRESS