The quirkiest and most unpredictable presidential race in decades has raised many questions: about the depth and duration of voter anger, about the power of insurgency and whether the old ways of campaigning and thinking of politics no longer hold true.
Some answers may finally begin to emerge Monday night here in Iowa, when voters will cast the first ballots of the 2016 campaign in a series of precinct-level meetings, or caucuses.
There are fiercely competitive contests on both sides.
Hillary Clinton, the Democratic front-runner whose 2008 campaign started unraveling with a third-place Iowa finish, faces an upstart challenge from Bernie Sanders, the democratic socialist senator from Vermont and a relatively recent addition to the party.
In the large Republican field, billionaire Donald Trump and Sen. Ted Cruz of Texas have battled for weeks for first place in Iowa polls, with Sen. Marco Rubio of Florida showing signs of a late surge.
Crowds swarmed candidates scurrying throughout Iowa on Sunday, volunteers and campaign organizers knocked on doors and dialed their way through voter contact lists, and a barrage of radio and TV ads — many of them scorchingly negative — provided a harsh soundtrack to an otherwise sunny and unseasonably mild day.
Clinton made her final full day of Iowa campaigning a family affair, stumping with her husband, former President Clinton, and their daughter, Chelsea. "I really love the fact that she brought my granddaughter with her to Des Moines," Hillary Clinton told a crowd in Council Bluffs. "I get to have a little time with Charlotte."
Sanders, who spent most of his career as an independent before seeking the Democratic nomination, exhorted Iowans to the polls, saying a victory over Clinton would rank among the biggest political upsets in recent history.
"If tomorrow night there is a large voter turnout, we win," Sanders told supporters in Marshalltown. "On the other hand, if there is a low voter turnout, we'll probably lose."
Trump tried to shore up his standing among Christian conservatives by attending a morning church service, then made a rare campaign appearance with his wife.
"Hello, Iowa, it's great to be here," Melania Trump told the crowd at a packed middle school gym in Council Bluffs before echoing her husband in her sales pitch: "He will be unbelievable — the best deal maker, the best master negotiator."
Cruz, who has slipped to second place in Iowa surveys, also kicked off Sunday with a visit to church with his wife and young daughters. The pastor urged politicians to debate the issues but not attack their enemies, and called on churchgoers to caucus Monday night.
Rubio wrapped up a nine-day blitz of the state by seeking to tamp down expectations. He feels good about his momentum, Rubio said in a classic formulation, but promised no more than a strong showing.
The results Monday will go a long way toward ordering the race, especially on the crowded GOP side. The next vote is just eight days later in New Hampshire, followed by contests in South Carolina and Nevada in this short month. The laggards in Iowa will have a tough time advancing, and for most of them, New Hampshire will amount to a last stand.
"For months, we've seen all these horse race polls, probably close to one a day," said Kevin Madden, a strategist for the last GOP nominee, Mitt Romney, but one who has stayed neutral in the 2016 contest. "Those will all go into the rearview mirror and candidate momentum will be based on actual voter judgments."
No candidate has been more disruptive, for good or ill, than Trump, the braggadocian New York billionaire who was greeted with eye-rolling when he burst into the contest last summer after repeatedly flirting with earlier runs. His actions — insulting opponents, women and minorities, picking fights with the party establishment and the powers at conservative Fox News — might have justified the skepticism.
But the serial controversies seemed only to raise Trump in the eyes of supporters, many of them freshly engaged in the political process, who see his make-your-own-rules style as refreshingly bold.
"I'm tired of politics as usual," said Republican Mike Walters, 61, who turned out last week for a boisterous Trump rally at a high school in Muscatine. "He's not going to say everything you like, but he's going to say it like it is."
The test will come Monday night, depending on whether people like Walters prove more interested in seeing the spectacle than taking the time to show their support for Trump at the caucuses.
Unlike voting in a primary, the meetings require a considerable investment of time and, even though the weather has been mild for an Iowa winter, the chance of snow and icy roads in the forecast may be enough to keep those less committed to their candidate from venturing out.
A second-place finish would be a blow to Trump, "taking away his most favorite talking point, which is how everyone loves him and he's a winner," said Stu Rothenberg, an independent analyst who has spent decades writing about campaigns and elections. "We don't know how he would act after losing."
But Cruz may have even more at stake in Iowa, a state that should be tailor-made for his appeal to evangelicals and strongly ideological Republicans, who make up the base of the party and historically reward candidates in Cruz's conservative mold.
"He's got a coalition built on people who caucus every four years like it's their job," said Matt Strawn, a former state GOP chairman who is unaligned in the race. "For Trump to be successful, he needs to remake the electorate into an image that is not of the Cruz coalition.
"And as trite as it is to say," Strawn said, "one thing we've learned … when it comes to Donald Trump, we're all going to have to find out together what's actually going to happen."
The dynamic is somewhat similar on the Democratic side, where Sanders has tapped a rich vein of discontent among liberals frustrated with President Obama and dubious of Clinton's ties to Wall Street as a former New York senator and her more hawkish defense and foreign policy views.
"He's young with his ideas. He's been super progressive since the '60s," said Dominic Tracy, 20, a political science student who recently went to see the senator from Vermont speak at the University of Northern Iowa. "I see him and I believe him. I don't believe Hillary."
Sanders has struck a particular chord among young people like Tracy, again raising the question of whether big crowds and buzz will translate into support Monday night. Young people are typically less likely to cast ballots than older voters, and their concentration in Iowa's college towns and urban areas could dilute their influence overall.
The third candidate on the Democratic side, former Maryland Gov. Martin O'Malley, has been present in Iowa longer this campaign than Clinton or Sanders but has never risen to the level of serious contender.
In the end, his greatest effect may come in defeat: Anyone supporting a candidate who garners less than 15% at a caucus must either join up with another candidate or go home, meaning the second choice of O'Malley voters could determine whether Clinton or Sanders wins.
Times staff writers Chris Megerian in Council Bluffs and Seema Mehta and Michael Finnegan in Des Moines contributed to this report.
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