A campaign sticker for Republican presidential candidate Mitt Romney is seen on a sign for Romney Street in London on Wednesday, as Romney arrived to meet with leaders, hold fundraisers and attend the opening of the Olympics. Charles Dharapak/AP hide caption

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Mitt Romney speaks at a campaign event in Bow, N.H., Friday. The campaigns have released their monthly financial reports, with Romney showing an advantage over President Obama. Charles Dharapak/AP hide caption

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Montana Attorney General Steve Bullock sought to prevent the U.S. Supreme Court's 2010 Citizens United decision from being used to strike down a state law restricting corporate campaign spending. On Monday, the Supreme Court rejected Bullock's argument, holding that "there can be no serious doubt" that Citizens United applies to Montana law. Matthew Brown/AP hide caption

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Justice Anthony Kennedy, who wrote the Citizens United opinion saying that corporations can pay for ads expressly promoting or attacking political candidates. Chip Somodevilla/Getty Images hide caption

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Screen grabs of four separate ads from four different political groups critical of President Obama's handling of Solyndra, the failed solar-panel maker. Clockwise from top left, the ads are from: Americans for Prosperity, MittRomney.com, American Crossroads and Crossroads GPS. hide caption

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Bill Koch (center) celebrates his team's 1992 America's Cup win. Koch, the brother of billionaire GOP donors Charles and David, has given $2 million to the superPAC backing Mitt Romney. Vince Bucci/AFP/Getty Images hide caption

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Former House Speaker Newt Gingrich pauses while announcing that he is suspending his presidential campaign Wednesday in Arlington, Va. Evan Vucci/AP hide caption

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Republican presidential candidate Mitt Romney greets supporters in Aston, Pa., on April 23. Jessica Kourkounis/Getty Images hide caption

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President Obama boards Air Force One at Andrews Air Force Base in Maryland, en route to Florida, on April 10. Whenever a president runs for re-election, his travel tends to become a political issue. Cliff Owen/AP hide caption

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Mitt Romney may like to say the president is out of ideas, but Obama's re-election campaign is definitely not out of money. Chip Somodevilla/Getty Images hide caption

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Selina Gray of Sanford, Fla., shows her sign at a rally protesting the death of Trayvon Martin, the unarmed teen shot by a neighborhood watch volunteer. Authorities have cited the state's "stand your ground" law as a reason charges have not been filed in Martin's death. Julie Fletcher/AP hide caption

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Foster Friess introduces Rick Santorum at the 2012 CPAC Conference in Washington, D.C., on Feb. 10 wearing a sweater vest embroidered with the candidate's name. Ron Sachs/CNP DPA/Landov hide caption

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