Hillary Clinton and Donald Trump hold narrow leads in the final "gold standard" poll in Iowa, a day before the state holds its caucuses, the official ballot that kickstarts the US presidential election.
The latest Des Moines Register/Bloomberg poll shows Mrs Clinton has a three-point lead over Vermont senator Bernie Sanders, in the Democratic campaign, a difference that falls within the margin of error.
The tight race between the two leading candidates remains largely unchanged from earlier this month. Mrs Clinton received 45 per cent, up 3 per cent, and Mr Sanders 42 per cent, up 2 per cent.
Former Maryland governor Martin O’Malley shed one percentage point, putting his support in the midwestern state at 2 per cent.
Mr Trump has a five-point edge on his closest rival, Texas senator Ted Cruz on the Republican side, regaining his lead in the poll. He has 28 per cent support - up six points from early January – compared with 23 per cent of Mr Cruz.
The billionaire New York businessman has turned the tables on the Texan. Mr Cruz led Mr Trump by 10 points in Iowa in December and that lead was narrowed to just two points earlier this month.
Florida senator Marco Rubio, who has emerged as the preferred candidate of the party's establishment, came third in the poll with 15 per cent, an increase of three points from early January.
Mr Rubio is followed by retired neurosurgeon Ben Carson with 10 per cent and Kentucky senator Rand Paul with 5 per cent. The other candidates all received support of less than 5 per cent.
Former Florida governor Jeb Bush had support of 2 per cent, putting him at the same level as undecided voters.
Voting in Iowa can be hard to predict because of the complicated caucus process and the unpredictability around turnout.
Tomorrow evening, voters will meet in groups across the state’s 1,681 precincts and hear stump speeches before picking nominees.
Registered Republicans vote by simply picking one candidate. On the Democratic side, supporters physically move to a designated area of their caucus site if they support one candidate. If any candidate fails to achieve 15 per cent of voters, their supporters can move elsewhere.
The Des Moines Register/Bloomberg survey was carried by pollster Ann Selzer, who has a track record of picking winners.
In the 2008 election, she predicted that Barack Obama would defeat Mrs Clinton despite other polls showing Mrs Clinton on average ahead.
The campaign team for Mr Sanders, who held a rally in front of almost 5,000 people in Iowa City last night, hailed the poll as it showed that his “come-from-nowhere” candidacy had turned into a too-close-to-call contest with Mrs Clinton, the one-time presumptive nominee.
Mr Sanders has a commanding lead in New Hampshire, which on February 9th will be the second state to vote, though he will struggle to beat her in South Carolina and Nevada where she has strong support among African-American and Hispanic American voters.
The possibility of heavy snowfall blanketing Iowa, forecast to arrive over the coming days, has raised concerns among candidates who fear that turnout would be badly affected, hurting breakaway candidates.
“Iowa does not want snow… I am against snow,” Mr Rubio joked at his final rally of the day last night in the Des Moines area.
The candidate’s events were well attended during the day as he hopes that a surprise on Monday evening could springboard the Florida senator into contention in the later nominating contests of other states.
"He is the most rational of the candidates," said Clayton Rae (18), a student visiting from Minnesota, at his rally in the Des Moines suburb of Urbandale. "Once some other candidates drop out, their followers will get behind Marco Rubio and then he is going to start surging."
Mrs Clinton received a boost on Saturday when the New York Times endorsed her. The newspaper described her as “one of the most broadly and deeply qualified presidential candidates in modern history.”
Mr Sanders “does not have the breadth of experience or policy ideas that Mrs Clinton offers,” said the editorial board of the Times.
Mr O’Malley is “a personable and reasonable liberal who seems more suited for the job he has already had – governor of Maryland and mayor of Baltimore – than for president,” said the newspaper.
On the Republican side, the newspaper could see no other candidate in a field of 11 other than Ohio governor John Kasich, who has barely figured in the national polls.
Mr Kasich, “though a distinct underdog, is the only plausible choice for Republicans tired of the extremism and inexperience on display in the race,” said the Times.
