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January 3 – The Iowa Republican caucuses are initially declared as a victory for Mitt Romney, however later counts show Rick Santorum with a small lead, however later counts show Ron Paul with a majority of delegates. The Iowa Democratic caucuses are won by Barack Obama. Neither caucus awards any delegates, but are to be used as a guide for delegate selection in June's party conventions.
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January 21 — The Nevada Democratic Caucuses are won by Barack Obama
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February 28 – Arizona Republican Primary won by Mitt Romney.
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April 3 – Maryland, Wisconsin, Washington DC primaries – won by Mitt Romney and Barack Obama, the latter of whom won enough delegates to win the Democratic nomination.
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May 5 – Former Governor of New Mexico Gary Johnson wins the presidential nomination of the Libertarian Party
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August 27–30 – Romney and Ryan are nominated for President and Vice President, respectively, at the 2012 Republican National Convention held in Tampa, Florida.
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September 3–6 – Obama and Biden are nominated for President and Vice President, respectively, at the 2012 Democratic National Convention was held in Charlotte, North Carolina
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December 17 – Electoral College formally elects a President and Vice President
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Inauguration Day
