Iowa caucuses: Republicans make final campaign push
Republican presidential hopefuls have toured Iowa on the last full day of campaigning before the Hawkeye State's caucuses kick-off the US election year.
Three contenders, Mitt Romney, Ron Paul and Rick Santorum, lead the pack ahead of Tuesday's vote.
But recent polls indicate many Iowans have still not decided who they want to vote for.
Iowa's ballot is the first contest to pick the Republican who will challenge Barack Obama for the White House.
Tuesday evening's caucuses will involve about 120,000 Iowans gathering in homes, schools and public buildings.
Spreading the message
As the vote neared, candidates spent Monday on a last-minute flurry of campaign events at coffee shops, pizza restaurants and hotel lobbies in an effort to to win over undecided voters.
Rick Santorum, a former Pennsylvania senator who has surged in Iowa polls in recent days, spoke in front of a packed house at a breakfast cafe in Polk City.
Despite concentrating almost exclusively on Iowa, Mr Santorum, a social conservative who appeals to Iowa's evangelical Christian voters, said his new-found popularity was helping his prospects for the long primary season to come.
"I would just say this, we've raised more money in the last few days than we've raised in the last few months," he said.
He has campaigned hard in every one of Iowa's 99 counties, impressing social conservatives with his message of rejecting gay marriage and abortion, even in cases of rape.
The beneficiary of a pre-Christmas poll surge, Texas Congressman Ron Paul restated his libertarian-tinged policies at campaign stops in Des Moines, Mason City and a series of other towns.
Mr Paul - the oldest candidate in the race, at 76 - returned to Iowa after spending the holiday weekend in Texas.
He has faced scrutiny over racially charged newsletters published in his name during the 1980s and 1990s.
Mr Paul - who wants an end to US military intervention overseas, and calls for the abolition of the Federal Reserve - said he had faith in his nationwide organisation, but conceded he needed a good result in Iowa.
A poor show in Iowa would be a "real challenge" for the campaign, he told the Associated Press. "We've invested a lot of time and money in doing well here."
In the city of Marion, front-runner Mitt Romney - whose 2008 campaign came unstuck in Iowa - exuded confidence.
"We're going to win this thing with all of our passion and strength," he said, before reprising his criticism of President Barack Obama.
"I want to see America united. I watch a president who's become a great divider, the great complainer, the great excuse-giver, the great blamer," Mr Romney said.
Mr Romney, a wealthy former businessman and governor of Massachusetts, has remained at or near the head of the pack throughout a long build-up to the primary campaign.
Persistent doubts about his conservative credentials have allowed others to remain in the hunt, though. Mr Santorum criticised Mr Romney on Monday, saying the nation needed a true commander-in-chief, not simply "executive experience".
Nevertheless, the former Massachusetts governor will win, analysts say, if the evangelical Christian vote is fragmented across competing conservative candidates - including Mr Santorum, Texas Governor Rick Perry and Minnesota Congresswoman Michele Bachmann.
Former House Speaker New Gingrich - whose own poll numbers surged spectacularly in November and early December - admitted on Monday that a barrage of attack advertisements had seriously eroded his support in Iowa.
At least $12.5m (£8.1m) has been spent on largely negative political advertising in Iowa in recent weeks.
"I don't think I'm going to win," he said, adding: "Whatever I do tomorrow night will be a victory because I am still standing."
Iowa experts say the state's weather could be a determining factor in voter turnout on Tuesday, with Mr Paul's dedicated supporters the most likely to brave poor conditions.
The forecast for Iowa on Tuesday is partly cloudy, BBC Weather says, with temperatures likely to hover just above freezing during the day.
A respected opinion poll published on Sunday by the Des Moines Register newspaper suggested Mr Romney remained the most popular candidate, with 25% support. Mr Paul was at 22%, while Mr Santorum scored 15%.
However, Mr Santorum's support is thought to have risen in recent days.
After Iowa, the state of New Hampshire holds its primary election on 10 January. Mitt Romney has a big lead there.
Former Utah Governor Jon Huntsman, who is also a Mormon, has skipped Iowa to campaign intensely in the Granite State.
Over the next six months, each US state will vote on the presidential contenders before a final nominee is selected.
The eventual Republican nominee will be anointed at the party convention in August before running in the 6 November general election against Democratic President Obama, who is seeking a second term.
Voters remain concerned by the slow pace of economic recovery from the recession that started during the end of the presidency of George W Bush and officially ended in 2009.