Jan. 2, 2008 — -- The first-in-the-nation Jan. 3 Iowa caucuses are tomorrow, and you may be wondering what all the fuss is about — and what exactly is a caucus, anyway?
Politically speaking, the Iowa caucuses are a big deal.
"The caucuses don't pick presidents, but they do reveal unexpected strengths and weaknesses of presidential candidates," said Dennis Goldford, professor of political science at Iowa's Drake University.
Thursday night's Iowa caucuses are poised to shake up what has become a too-close-to-call presidential nominating contest for both the Democrats and Republicans.
Knowing the Iowa caucuses could make or break their candidacy, many Democratic and Republican frontrunners are throwing everything they've got at the Hawkeye State.
Historically, a win in Iowa has cemented a candidate's status as a presidential contender, attracted positive media attention, and convinced fundraising donors to open their wallets.
A strong showing in Iowa could also slingshot an obscure candidate to the nomination, or even all the way to the White House.
But a poor outcome could crush the presidential aspirations of White House wannabes, making it difficult to ever regain political momentum.
The fate of the candidates Thursday night rests with Iowa caucus-goers, who will gather in Iowa's 99 counties to select the candidate they would like to win their party's nomination.
Unlike primaries, where machines count the votes, the Iowa caucuses are intimate and dynamic, with caucus-goers clustering in public schools, town halls, church basements and private homes.
Caucus-goers take their roles as potential king makers very seriously.
"Meeting the candidates gives you a firsthand personality check," said Tina Kastendidck, a Republican precinct chair, and high school teacher from Fort Dodge, Iowa.
Iowa voters have unparalleled access to the candidates, seeing some of them multiple times, up close at campaign rallies, town hall meetings, and even at a neighbor's kitchen table.
Kastendidck has personally met every presidential candidate, except for Sen. John McCain, R-Ariz.
"You can tell if they're a career politician or not," she said.
Iowa's political parties adopted the caucus system in 1846, but they were obscure local events, held in March or April.
It wasn't until 1972 that Iowa received its first-in-the-nation status. To encourage greater participation in the elections, Democratic Party leaders decided to hold the caucuses early in January.
That same year, Sen. George McGovern, D-S.D., took advantage of the early caucus date and organized and campaigned heavily in the state, finishing a strong second.
With momentum and media attention giving his candidacy a bounce, McGovern went on to win his party's nomination.
Four years later, an unknown peanut farmer from Georgia, named Jimmy Carter, ran a low budget caucus campaign in Iowa in 1976. Carter used his surprise second place finish to go on to win the Democratic nomination, and eventually won the White House.
However, far more candidates have found their White House aspirations squashed after the early votes.
In the history of the Iowa caucuses, no candidate who has finished worse than third among the candidates, has ever gone on to win the nomination.
For the Democratic contenders, being the second choice of Iowa voters could be as important as being their first pick.
That's because of the unique Iowa Democratic Party "viability" rule.
"In 80 percent of the 1,781 Democratic precincts in Iowa, the candidate needs the support of at least 15 percent of the caucus voters," said Carrie Giddins, Iowa Democratic Party communications director.
If candidates do not reach 15 percent, their supporters have the opportunity to throw their votes to a more viable contender.
Another distinctive feature of the Democratic caucuses is that it pays to have support throughout Iowa's 99 counties and 1,781 precincts.
Because of the rules and formulas used to apportion delegates, a candidate gets no extra benefit from overwhelming support in a precinct.
Not so for Iowa Republicans, however.
The Republican caucuses in Iowa don't have a viability threshold. Under the Republican Party of Iowa "one head, one vote" system, each caucus voter's pick is recorded.
All of that makes the Iowa caucuses unique and special.
"Iowa caucus-goers vet these candidates for the rest of the country," Goldford said. "For candidates, the caucuses offer them a relatively inexpensive means to establish themselves as a potential presidential nominee."
ABC News' Teddy Davis contributed to this report.