As the first voters of 2016, Iowans play an outsize role in shaping the presidential primary races. A strong finish in the caucuses can help propel a candidate to the nomination; a poor performance usually spells disaster.

Even so, only one in five registered voters in Iowa shows up to caucus, leaving just a sliver of partisan activists to anoint the early front-runners and winnow the primary field.

“Americans talk a lot about the right to vote, but we don’t actually mean it,” said Dennis Goldford, a political science professor at Drake University in Des Moines who studies voter turnout in Iowa. “Part of the issue is the general American disinclination to be involved in voting and elections.”

Low voter turnout isn’t unique to the Iowa caucuses. In 2012, average turnout in the 41 states that held Democratic and Republican presidential primaries was just 17.3 percent, according to an analysis by the Bipartisan Policy Center — the lowest total since 1972.

But the trend stands out in Iowa, considering the state’s position in the primary calendar. While every vote counts, there are few states, if any, where an individual vote has as much of an impact. (Remember, President Obama won Iowa in 2008, defying expectations and propelling him to the nomination. John Kerry, too, won Iowa in 2004 and went on to clinch the nomination.)

Still, turnout there remains surprisingly low.

In 2012, 121,503 Republicans — or 19.7 percent of the state’s 614,913 registered GOP voters — participated in the caucus. The low turnout rate applies to both parties: In 2004, 23.3 percent of registered Democrats in the state cast a ballot.

The one recent exception was 2008, when there was unusual excitement on the left surrounding Barack Obama and Hillary Clinton’s barrier-breaking campaigns. That year, 239,872 Iowa Democrats — or 39.5 percent of the state’s registered Democratic voters — participated in the party’s caucus.

However, the record turnout in 2008 also included independents who registered as Democrats to vote in the party’s caucus.

Unlike New Hampshire and other states with “open” primary systems where independents can vote for any candidate, the Iowa caucuses are only open to registered members of the Democratic and Republican parties. The turnout each election cycle includes independents who change their party affiliation for the caucus, which artificially inflates the parties’ overall voting totals.

For voters across the political spectrum, participating in the Iowa caucuses is typically a bigger time commitment than voting in a primary, where all that is required is waiting in line, (which can sometimes take several hours,) and casting a ballot.

The Iowa caucuses, which are held at local precincts across the state, involve spirited debates and can lead to multiple rounds of balloting if a precinct’s voters cannot come to a consensus on a candidate on the first try.

Attending a caucus eats up the evening, making it hard for people who might like to participate but can’t rearrange their busy schedules to make time for a political event.

“You have to hope the car starts, the babysitter shows up, you’re not sick and there’s no blizzard,” said Goldford, adding that it’s especially difficult for people who work at night and can’t take off for the caucuses, which start at 7 p.m.

As a result, the caucuses are dominated by Iowa’s most engaged primary voters — a small subset of liberals and religious conservatives in a largely white, rural state that is far less diverse than the country as a whole.

“There are issues about how representative the voters of Iowa are,” said Thomas Patterson, an expert on U.S. politics who teaches at Harvard’s John F. Kennedy School of Government. “But you can make that argument about any state.”

The focus on voter turnout will intensify as the candidates spread out across Iowa ahead of Monday’s caucuses.

Republican front-runner Donald Trump and Sen. Bernie Sanders of Vermont could benefit the most from an above-average turnout. Sen. Ted Cruz of Texas is hoping for a large turnout from evangelical voters to help him surge past Trump.

At a Cruz campaign event in Iowa Tuesday, former Texas Governor Rick Perry reminded voters that they play a special role in the election — if they choose to participate.

“Iowa,” Perry said, “is at the epicenter of a decision that will have monumental effect on this country.”