For over 40 years, the Iowa caucuses have been a launching pad for some presidential candidates to secure the party's nomination.
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But while they have been the source of elation for some, they have dashed the aspirations of other presidential hopefuls, or often totally surprising the general public.
Here are some of the most memorable results from Iowa's caucuses through the decades:
On caucus night, the Iowa GOP declared Mitt Romney, who ultimately became the party's nominee, the winner by eight votes. But 16 days later, the party changed the result, declaring Rick Santorum the victor by 34 votes. Party officials said they hadn’t gotten results from eight precincts, and those precincts changed the standing. Partially as a result, the Iowa GOP is now working with Microsoft to launch an app this year to remedy past counting issues.
Barack Obama, then a junior senator from Illinois, won Iowa by 8 percentage points, soundly defeating John Edwards and Hillary Clinton in the Democratic primary. Obama had previously been seen as the underdog, and Clinton as the inevitable nominee. Although he would go on to lose New Hampshire, the Iowa victory launched him into a contested nomination fight with Clinton that lasted until June.
Howard Dean was the Democratic front-runner and top fundraiser up until the Iowa caucuses. He finished a distant third behind John Kerry and John Edwards. In his speech to supporters following the results, he let out a legendary scream that is still remembered 12 years later. He dropped out six weeks after the caucuses.
Donald Trump isn't the only front-runner to skip a debate right before the caucuses. In 1980, then-candidate Ronald Reagan did the same thing. Reagan, who was favored to win, was narrowly defeated by George H.W. Bush, 29.5 percent to 31.6 percent. Reagan ultimately won the nomination, selecting Bush as his vice president.
Although “uncommitted” got more votes than Jimmy Carter (37.2 percent to 27.6 percent), Carter got more votes than any other Democratic candidate. Birch Bayh got 13.2 percent. Carter’s Iowa victory helped propel him to the Democratic nomination, after being considered a long shot when he launched his bid.