Since 1972, the Iowa caucuses have been the first time Americans vote for a potential president.

The outcome can change presidential races. The winner gets a spurt of momentum and media attention. But the majority have not gone on to be president.

Only three politicians have won a contested Iowa caucus and become president — Jimmy Carter, George W. Bush, and Barack Obama.

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Iowa is no guarantee, but it promises momentum.

The Iowa caucuses, which have only been around since 1972, are the first time voters have a say in who could be the next president. As Alex Altman wrote for Time, "Iowa is the kind of place where a candidate can win on sweat and gas money." This year's Iowa caucuses are on Monday night.

Only three politicians have won a contested Iowa caucus and become president — Jimmy Carter, George W. Bush, and Barack Obama.

But 15 others have won Iowa and not become president. The other times, sitting presidents won the caucuses when they were running unopposed, or with little competition.

Carter's 1976 presidential run was the first time the Iowa caucuses changed everything. He campaigned vigorously on the ground, and by winning Iowa, he turned an unlikely run into a successful presidential campaign by harnessing the media's attention.

It happened again in the 2008 election. Before the caucuses, Obama was trailing Hillary Clinton, but the early victory was enough to bolster his reputation, and by Super Tuesday, he had taken the lead in polls.

Here are all of the contested Iowa caucus winners and what happened to them after winning.