Republican presidential candidate Mitt Romney, joined by Sen. Marco Rubio, R-Fla., talks to reporters during a news conference in Aston, Pa., on Monday. Rubio is frequently mentioned as a potential running mate for Romney. Jae C. Hong/AP hide caption

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Ann Romney, wife of Republican presidential candidate Mitt Romney, speaks at his Nevada caucus victory celebration in Las Vegas on Feb. 4. Gerald Herbert/AP hide caption

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Mitt Romney jokes with Wisconsin Rep. Paul Ryan during a pancake brunch on April 1 in Milwaukee. Justin Sullivan/Getty Images hide caption

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Massachusetts Gov. Mitt Romney signs into law a new health care reform bill during an April 12, 2006, ceremony at Faneuil Hall in Boston. The bill made Massachusetts the first state in the country to require that all residents have health insurance and has become a centerpiece of criticisms leveled by Romney's opponents in the 2012 presidential race. Joe Raedle/Getty Images hide caption

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Sen. Jim DeMint, R-S.C., center, joins other conservative lawmakers on Capitol Hill to criticize President Obama's health care law on Oct. 5, 2011. They said the boxes were packed with petitions asking Congress to repeal the Affordable Care Act. J. Scott Applewhite/AP hide caption

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President Obama and first lady Michelle Obama listen as a choir performs during the groundbreaking ceremony for the Smithsonian National Museum of African American History and Culture in Washington, D.C., on Wednesday. Saul Loeb/AFP/Getty Images hide caption

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