After a long year of campaigning, Republican and Democratic presidential candidates face voters for the first time, battling in Iowa Monday for a boost toward the White House — or in many cases, simply a reason to stay in the race.

The contests in both parties were tight heading into the evening caucuses. Among Republicans, billionaire Donald Trump appeared to have a slim edge over Texas Sen. Ted Cruz. Hillary Clinton and Vermont Sen. Bernie Sanders were locked in an unexpectedly close Democratic contest, reviving memories of the former secretary of state’s disappointing showing in Iowa eight years ago.

“We knocked on 125,000 doors this past weekend,” Clinton told NBC’s “Today” show. “Although it’s a tight race, a lot of the people who are committed to caucusing for me will be there and standing up for me and I will do the same for them in the campaign and in the presidency.”

Sanders, the Vermont senator who has been generating big, youthful crowds across the state, urged voters to help him “make history” with a win in Iowa.

“We will struggle tonight if the voter turnout is low. That’s a fact,” Sanders told volunteers and supporters in Des Moines.

Candidates face an electorate deeply frustrated with Washington. While the economy has approved under President Barack Obama’s watch, the recovery has eluded many Americans. New terror threats at home and abroad have also ratcheted up national security concerns.

In Iowa, which has for decades launched the presidential nominating contest, candidates also face an electorate that’s less diverse than the country as a whole.

Iowa has decidedly mixed results in picking the parties’ eventual nominees. The past two Republican caucus winners — former Arkansas Gov. Mike Huckabee and former Pennsylvania Sen. Rick Santorum — faded as the race stretched on. But Obama’s unexpected 2008 victory was instrumental in his path to the Democratic nomination, easing the anxieties of those who worried the young black senator would struggle to win white voters.

Iowa is whiter, more rural and more evangelical in its voting than many states. But, given its prime leadoff spot in the primary season, it gets extra attention from presidential campaigns.

Monday’s contest will offer the first hard evidence of whether Trump can turn the legion of fans drawn to his plainspoken populism into voters. He has intensified his campaign schedule during the final sprint, including a pair of rallies Monday.

Cruz has modeled his campaign after past Iowa winners, visiting all of the state’s 99 counties and courting influential evangelical and conservative leaders. With the state seemingly tailor-made for his brand of uncompromising conservatism, a loss to Trump would likely be viewed as a failure to meet expectations.

Seeking to tamp down expectations, Cruz said Sunday he was pleased just to be in the mix for first place.

“If you had told me a year ago that two days out from the Iowa caucuses we would be neck and neck, effectively tied for first place in the state of Iowa, I would have been thrilled,” Cruz said.

Cruz has spent the closing days of the Iowa campaign focused intensely on Marco Rubio, trying to ensure the Florida senator doesn’t inch into second place. Rubio is viewed by many Republicans as a more mainstream alternative to Trump and Cruz, though he’ll need to stay competitive in Iowa in order to maintain his viability.

Rubio, who previously lashed back at criticism, adopted the same reflective tone as many of his rivals on Monday, telling NBC that Cruz “has a very strong ground game.” He dismissed attacks against him as “politics as usual.”

The campaigns were anxiously keeping an eye on the weather. A snowfall forecast to start Monday night appeared more likely to hinder the hopefuls in their rush out of Iowa than the voters. Republican John Kasich already had decamped to New Hampshire, with New Jersey Gov. Chris Christie and former Florida Gov. Jeb Bush following behind Monday afternoon, hours before the caucuses started.

The trio of governors has had a light footprint in Iowa, banking instead on strong showings in New Hampshire’s Feb. 9 primary to jumpstart their White House bids. Yet some Republican leaders worry that if Trump or Cruz pull off a big victory in Iowa, it could be difficult to slow their momentum.

Bush, for example, started the year as a fundraising juggernaut. But according to records released Sunday, both his super PAC and personal campaign fundraising declined significantly in the later months of 2015 as he struggled to keep up with Trump.

Unlike in primaries, where voters can cast their ballots throughout the day, the caucuses begin across Iowa at 7 p.m. CST. Democrats will gather at 1,100 locations and Republicans at nearly 900 spots.

The Iowa Republican Party expected turnout to top the previous record of 120,000 people in 2012. Democrats also expected a strong turnout, though not nearly as large as the record-setting 240,000 who caucused in the 2008 contest between Clinton, Barack Obama and John Edwards.

While both parties caucus on the same night, they do so with different rules.

Republicans vote by private ballot. The state’s 30 Republican delegates are awarded proportionally based on the stateside vote.

Democrats take a more interactive approach, with voters forming groups and publicly declaring their support for a candidate. If the number of people in any group is less than 15 percent of the total, they can either choose not to participate or can join another viable candidate’s group.

Those numbers are awarded proportionately, based on statewide and congressional district voting, as Iowa Democrats determine their 44 delegates to the national convention.

(AP)