Jeb Bush speaks to an audience of voters on Feb. 18 in Columbia, S.C. Bush dropped out of the GOP presidential race two days later, after finishing a distant fourth in the state's primary. Spencer Platt/Getty Images hide caption

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Republican presidential candidates at the final GOP before the South Carolina primary on Saturday at the Peace Center in Greenville, S.C. Spencer Platt/Getty Images hide caption

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Bernie Sanders and Donald Trump deliver victory speeches at their respective watch parties in New Hampshire. Jewel Samad/AFP; Joe Raedle/Getty Images hide caption

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Republican Chris Christie of New Jersey has invested nearly his entire campaign on New Hampshire. A poor result will almost certainly effectively end his candidacy. Robert F. Bukaty/AP hide caption

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