Former Secretary of State Hillary Clinton ducks after a woman threw a shoe at her while she was delivering remarks at the Institute of Scrap Recycling Industries conference on Thursday in Las Vegas. Isaac Brekken/Getty Images hide caption

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Former Secretary of State Hillary Rodham Clinton and former President Clinton huddle under an umbrella during inaugural ceremonies for Virginia Gov. Terry McAuliffe in Richmond on Jan. 11. Patrick Semansky/AP hide caption

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The question isn't whether former Secretary of State Hillary Clinton will run for president in 2016 but whether she will stop, say the authors of a new book. Gerald Herbert/AP hide caption

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Then-Secretary of State Hillary Clinton and Vice President Biden at a White House event in October 2011. A new book says President Obama's aides were then studying whether to replace Biden with the former first lady on the 2012 ticket. Kevin Dietsch /UPI /Landov hide caption

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George Soros, seen at a forum in Berlin last year, joined a superPAC backing a Hillary Clinton presidential run in 2016. Sean Gallup/Getty Images hide caption

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Hilary Clinton at last week's Clinton Global Initiative forum in in New York City. /PA Photos/Landov hide caption

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