President Richard Nixon tells reporters he will not allow his legal counsel, John Dean, to testify before Congress in the Watergate investigation, March 15, 1973. Leaks about the Watergate break-in eventually helped lead to Nixon's resignation. And his administration fought and lost a Supreme Court battle over leaking of the so-called Pentagon Papers about Vietnam. Charles Tasnadi/AP hide caption

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President Obama climbs the podium to give a media briefing at the end of a NATO summit in Lisbon, Portugal, on Nov. 20, 2010. Markus Schreiber/AP hide caption

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Democratic presidential candidate Sen. John Kerry debates President George W. Bush on Oct. 13, 2004. Bush later won re-election. Rick T. Wilking/AP hide caption

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Protesters in Nice, France, hold banners depicting then-French President Nicolas Sarkozy and President Obama before a November 2011 G-20 summit where global financial issues were discussed. Sarkozy has since lost re-election; some political scientists say economic problems in Europe also could play an unprecedented role in the upcoming U.S. election. Frederic Nebinger/Getty Images hide caption

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President Franklin D. Roosevelt and his Republican challenger, Kansas Gov. Alfred M. Landon (left), meet in September 1936. AP hide caption

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An unidentified heckler lets loose as President Obama begins a speech at the Martin Luther King memorial dedication in Washington, D.C., in October 2011. Mannie Garcia/UPI/Landov hide caption

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While American politicians may be scripted, they're not this robotic. But whoever wins the presidency this year will preside over a U.S. economy where automation is becoming increasingly important. iStockphoto hide caption

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The infield at Churchill Downs can get pretty beer-soaked, as this scene from the 2011 Kentucky Derby proves. But this year, things could get even more crazy: The Derby falls on another of America's favorite "alcoholidays," Cinco de Mayo. Matt Slocum/AP hide caption

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Former Massachusetts Gov. Mitt Romney and President Obama will spend the next six months highlighting their differences. But they also share some striking similarities. Chip Somodevilla/Olivier Douliery/Getty Images hide caption

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Republican presidential hopeful Ronald Reagan, right, listens to the Rev. Jerry Falwell during a campaign stop in Lynchburg, Va., in October 198 Charles Harrity/AP hide caption

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