DES MOINES, Iowa Donald Trump's ground-breaking White House campaign faces a moment of truth on Monday when Iowa voters begin the nationwide process of choosing a new U.S. president, with polls showing him in a tight battle with Ted Cruz to be the Republican nominee.
On the Democratic side, front-runner Hillary Clinton is hoping to fend off a stiff challenge in Iowa from insurgent Bernie Sanders in the first of the state-by-state battles to pick party candidates for the Nov. 8 election to succeed President Barack Obama.
Late opinion polls showed Trump, a blunt-spoken billionaire businessman who has never held public office, with a small lead over Cruz, a conservative U.S. senator from Texas. Clinton had a slight edge on Sanders, a U.S. senator from Vermont.
But there is a large bloc of undecided voters in both parties in Iowa and no certainty on who will turn up at the caucuses on a wintry evening, given that many supporters of Trump and Sanders are new to the process and disenchanted with traditional politics.
A Des Moines Register/Bloomberg Iowa poll on Saturday showed three in 10 likely Democratic caucus-goers and 45 percent of likely Republican caucus-goers were still uncertain.
Iowans will begin choosing candidates at 7 p.m. CST (0100 GMT on Tuesday), with results expected within a few hours.
The caucuses will be the first time Trump, a real estate tycoon and former reality TV star, has had to translate his political appeal into votes.
A win could validate an aggressive campaign that has alarmed the Republican establishment, dwarfed the efforts of many seasoned politicians and has been marked by controversies such as his calls for a temporary ban on Muslims entering the United States and for a wall along the Mexican border.
A loss would dent Trump's carefully cultivated campaign persona as a "winner" and create immense pressure for a better performance in the next nominating contests - in New Hampshire and South Carolina - later this month.
'TAKING OUR COUNTRY BACK'
Trump started the day with a rally in Waterloo, Iowa, telling the crowd while he is leading all the polls, none mattered now if they did not attend caucuses.
"Tonight is so important: this is the beginning of taking our country back," said Trump, who has attracted large crowds in Iowa with his mix of populism and scathing criticism of opponents. "I learnt how much people love our country, they love our country. When I see what's going on it's just incredible."
The Iowa caucuses, which give the Midwestern state a political influence far greater than its population of just 3 million would suggest, kick off a process that leads to the parties' formal presidential nominations this summer.
The caucuses are a long and sometimes arcane ritual, taking place in 1,100 schools, churches and other public locations across the Midwestern state. At least two Republican caucuses will be in private homes and a Democratic one will take place at an equestrian centre.
White House hopefuls descend on the state early and often and give people the chance to see them up close, meaning many Iowans are slow to decide who to back.
"I'm still checking them out. The field is large and it requires some thought," said Paul Albritton of Carlisle, Iowa, a training coordinator at Iowa State University, as he waited to see U.S. Senator Marco Rubio of Florida last week. "I'm thinking about who can win in November."
For the winners in Iowa, the prize will be valuable momentum that could stretch for months, while many of the losers on the Republican side could quickly begin dropping by the wayside.
The 2016 election is shaping up to be the year of angry voters as disgruntled Americans worry about issues such as immigration, terrorism, income inequality and healthcare, fuelling the campaigns of Trump and self-declared democratic socialist Sanders.
Some 73 percent of voters likely to head to the polls in November's election say they think the country is on the wrong track, according to a Reuters/Ipsos poll last month.
On the Republican side, opinion polls show foreign policy hawk Rubio might win third place in Iowa and stake a claim as the best hope for the party's mainstream.
"We're not the front-runner in Iowa, we've known this," Rubio said on NBC's "Today" show on Monday, trying to keep expectations tamped down. "But we feel good about our campaign. We know it's an uphill climb, but we're fighting hard. We're working hard."
For the Democrats, Clinton needs a win in Iowa to prevent a potential two-state opening losing streak that would raise fresh questions about a candidate who was considered the clear front-runner just two months ago.
Clinton, a former secretary of state and U.S. senator, often touts her years of experience in politics, and says she will defend much of Obama's legacy. Sanders has attacked from the left, saying he would do more than Clinton to take on Wall Street excesses and to help American workers who feel left behind by the slow economic recovery.
Clinton lost Iowa in 2008 and went on to lose a protracted primary battle to Obama. She told ABC's "Good Morning America" programme that it would be different this time.
"I have a much better organization, to be just really clear about it. I think we built an organization using a lot of the lessons learnt ... I think I'm a better candidate," she said.
Some candidates have tried to position themselves as the anti-anger candidate.
"It seems like it's almost as if people don't want you to be able to govern, they just want you to be able to throw rocks and break glass," Republican Mike Huckabee said Monday on CNN.
"If that's the case, I'm probably not their guy," said Huckabee, who won the 2008 Republican Iowa caucus, but has struggled to gain any traction this time.
(Additional reporting by Steve Holland and Ginger Gibson in Iowa; Writing by Alistair Bell; Editing by Caren Bohan, Peter Cooney and Frances Kerry)
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