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.