What do Bill Clinton, George H.W. Bush and Ronald Reagan have in common?
These former presidents all lost in the Iowa caucuses, but won their party's nomination and, of course, the subsequent general elections.
What about Mike Huckabee, Dick Gephardt and Tom Harkin? They came in first in Iowa but failed to become their party's standard-bearer.
Iowa has always chosen its presidential candidates using caucuses, but the caucuses didn't achieve the significance currently attributed to them until 1972, when the Democratic Party moved the contest to the beginning of the year.
Since then, however, only three non-incumbent candidates who won Iowa have gone on to win the presidency.
Seven democrats in 10 caucuses who won in Iowa have ended up winning their party's nomination, according to the Des Moines Register. (Two were incumbents who ran unopposed.)
Six Republican winners in Iowa, out of nine contests there, have gone on to win the GOP nomination. (Three were incumbents who ran unopposed.)
So a win in Iowa can give a candidate momentum, but by no means guarantees the party's nomination.
But Bloomberg Businessweek's Greg Giroux adds that the Iowa caucus is also known for ending presidential campaigns, so we may see some campaigns go the way of Hermain Cain's after Wednesday's voting. In fact, since 1972, no candidate who has finished worse than fourth place in Iowa has won the Democratic or Republican nomination.
As of Tuesday evening, polls show Mitt Romney, Ron Paul, and Rick Santorum in a virtual dead heat.
Click here for more about how the Iowa caucuses work.
Click through the slideshow to check out some of the winners of past Iowa caucuses:
Mike Huckabee (R) won the Iowa caucus, beating out Mitt Romney, who won the Iowa Ames Straw Poll that year. John McCain, the eventual Republican nominee, came in fourth with just 13 percent of the vote. He is the only candidate since 1972 to win his party's nomination after such a low finish in Iowa. Barack Obama (D) won the Iowa caucus and went on to win the Democratic nomination and the presidency. Obama was only the third non-incumbent candidate to win all three contests.
George W. Bush (R) was the incumbent president. John Kerry (D) won the Iowa caucus and went on to win his party's nomination. Kerry eventually lost a close general election to Bush.
George W. Bush (R) won the Iowa caucus and went on to win the GOP nomination and the presidency. Al Gore (D) won the Iowa caucus by a wide margin and also won the Democratic nomination. Gore lost the presidential election in very close race with Bush.
Bob Dole (R) won the Iowa caucus and the GOP nomination, but lost the presidency to Bill Clinton's re-election bid. Bill Clinton (D) was the incumbent president.
George H.W. Bush (R) was the incumbent president. Tom Harkin (D) won the caucus in his home state of Iowa with a sweeping 76 percent of the vote -- none of the other Democratic candidates even chose to participate. Harkin ended up losing the Democratic nomination to Bill Clinton, who went on to win the presidency.
Bob Dole (R) won the Iowa caucus but lost the GOP nomination. George H.W. Bush, the eventual nominee and winner of the presidency, came in third in Iowa. Dick Gephardt (D) won the Iowa caucus but lost the Democratic nomination to Michael Dukakis, who also came in third in the caucus that year.
Ronald Reagan (R) was the incumbent president. Walter Mondale (D) won the Iowa caucus and the Democratic nomination. He lost the general election to Reagan.
George H.W. Bush (R) won the Iowa caucus, but lost the GOP nomination to Ronald Reagan, who went on to win the presidency. Jimmy Carter (D), the incumbent president, was challenged in the Democratic primary by Ted Kennedy. Carter defeated Kennedy in the Iowa caucus and sealed his party's nomination. Carter lost the presidency to Reagan.
Gerald Ford (R), after inheriting the presidency following the Watergate scandal, won the Iowa caucus and the GOP nomination. He lost the general election to Jimmy Carter. Jimmy Carter (D) rose from obscurity to win the Iowa caucus, the Democratic nomination and the presidency. He was the first person to win all three contests. (AP image)
Edmund Muskie (D) won the Iowa caucus (technically he placed just behind "uncommitted") but lost the Democratic nomination to George McGovern, who came in second in Iowa. McGovern lost the general election to Richard Nixon. The Republican Party moved its Iowa caucus to the first spot in 1976.