DES MOINES, Iowa — A new phase in the fight for the Republican Party's soul begins Monday night as Iowa voters decide whether they prefer Donald Trump's aggressive populist politics or Ted Cruz's fiery conservativism in the GOP's opening presidential primary contest of 2016.
While only a first step, Iowa's decision will play prominently in shaping the Republican election. As Trump and Cruz eye first place, Florida Sen. Marco Rubio is working to emerge as the clear favorite in his party's mainstream wing, which fears both Cruz and Trump would be a disaster in a general election matchup against the Democratic nominee.
The results in Iowa may also narrow what has been an unusually crowded Republican field with a number of candidates struggling to achieve the turnout needed to continue.
Caucusing begins across Iowa at 7 p.m. CST.
"We're feeling really good," Trump said Monday morning on MSNBC's "Morning Joe."
"I can't tell you what's going to happen because it's an election, and the only poll that matters is the poll that's going to start in a little while," the billionaire businessman said, adding, "The day has finally arrived where we begin this really incredible process."
Trump drew smaller crowds than usual on Monday as he tried to rally support hours before the caucuses began. There were dozens of empty chairs at his first event on a foggy morning in Waterloo, Iowa. He predicted victory at a subsequent appearance with former Alaska Gov. Sarah Palin at his side.
Cruz sought to tamp down expectations in a state seemingly tailor-made for his brand of uncompromising conservatism, saying the day before that he's just pleased 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," said the Texas senator.
Cruz's campaign has spent the closing days of the Iowa contest attacking Rubio to help ensure the Florida senator doesn't inch into second place. Many Republicans view Rubio as a more mainstream alternative to Trump and Cruz, though his viability will depend on staying competitive in Iowa.
Rubio in recent days lashed back at the many attacks aimed in his direction, but adopted the same reflective tone as many of his rivals in the campaign's final hours, telling NBC that Cruz "has a very strong ground game." He dismissed the attacks against him as "politics as usual."
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. The scope of the billionaire's organization in Iowa is a mystery, though Trump himself has intensified his campaign schedule during the final sprint.
Cruz has modeled his campaign after past Iowa winners, visiting all of the state's 99 counties and courting influential evangelical and conservative leaders.
Meanwhile, former Florida Gov. Jeb Bush, New Jersey Gov. Chris Christie and Ohio Gov. John Kasich barely register in recent Iowa polls. The trio of governors is banking instead on strong showings in New Hampshire's Feb. 9 primary to jumpstart their White House bids.
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.
Yet some Republican leaders worry that if Trump or Cruz pull off a big victory in Iowa, it would be difficult to slow their momentum.
Conservative commentator Glenn Beck, a Cruz supporter, warned last week that a Trump victory would trigger "a snowball to hell."
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AP writer Jill Colvin in Waterloo, Iowa contributed to this report.