Polling shows no clear frontrunner in tight race as four Democratic candidates are knotted together at the top

After a year of ideological clashes and policy debates, voters in Iowa are set to have their say on which Democratic presidential candidate they believe is best positioned to beat Donald Trump in November.

'Nerve-racking': Iowans under pressure on eve of crucial caucuses Read more

Hundreds of thousands of Iowans – many of them still undecided – will gather on Monday night in gymnasiums, libraries and churches to participate in the Iowa caucuses, the first official nominating contest of the 2020 primary.

On the final day of campaigning, candidates blanketed the state, speaking to overcrowded rallies, overflow rooms and packed campaign offices in a final push to persuade the nearly 50% of caucus-goers who say they may still change their minds.

The race remains fluid with no clear frontrunner. Recent polls show four of the 11 remaining candidates knotted together at the top – former vice-president Joe Biden, Vermont senator Bernie Sanders, Massachusetts senator Elizabeth Warren and former South Bend, Indiana mayor Pete Buttigieg.

Q&A What are the Iowa caucuses? Show Hide On 3 February, the midwestern state of Iowa will kick off the long process of choosing the Democratic party’s presidential nominee, who will take on Donald Trump in the US election in November. Most US states hold primary elections, in which voters go to a polling place, mail in their ballots or otherwise vote remotely. But a handful of states hold caucuses – complicated, hours-long meetings with multiple rounds of balloting until one candidate emerges as victor. Both Democratic and Republican caucuses will take place on 3 February. But because Trump doesn't face any serious Republican challengers, all eyes will be on the Democratic contest. Put simply, Iowans aged 18 (at the time of the November 3 election) and over who are registered Democrats will gather in caucus sites (school gyms, churches, community halls) in their designated precinct, and vote with their feet by splitting into groups based on their preferred candidate. Once voting is over at a caucus site, the support for viable candidates (those with more than 15% of the votes) is translated into a number of “state delegate equivalents”. That result is used to calculate the number of national delegates each candidate receives. National delegates eventually choose the nominee at the Democratic convention in July. On the night, the candidate with the most SDEs is considered the winner. Photograph: Jim Watson/AFP

Iowans famously take their responsibility seriously: since 2000, every Democratic winner of the caucuses has gone on to win the nomination. But the prospect of four more years of a president Democratic voters view as singularly dangerous has added to the pressure. They could award one candidate – or possibly many – an early advantage as they compete in primaries across the rest of the nation.

“I respectfully suggest, not because I’m running, but because of the man who’s president, you’ve never had a greater responsibility than you have today,” Biden told more than a thousand people his at his final rally on Sunday, in a Des Moines middle school gym.

Facebook Twitter Pinterest Joe Biden campaigning in Dubuque, Iowa, on Sunday. Photograph: Jim Lo Scalzo/EPA

Across the state there was a growing sense that Sanders had taken the lead while the other frontrunners were locked into a battle for second. A highly anticipated Des Moines Register/CNN/Mediacom poll that might have shed some clarity was canceled on Saturday night due to concerns with its methodology.

“Our politics is the only way we can beat Donald Trump, the most dangerous president in modern American history,” Sanders told volunteers at a field office in Newton on Sunday. “And the only way we can be him is if we have the largest voter turnout that this country has ever seen.”

Sanders’ strength has alarmed some Democrats who believe nominating a self-described socialist would be a disaster. One group spent nearly $700,000 on television ads in Iowa questioning Sanders’ electability.

On Sunday, an NBC News reporter overheard John Kerry, the 2004 Democratic presidential nominee and a top Biden surrogate, speculating that he might enter the race to avert “the possibility of Bernie Sanders taking down the Democratic party – down whole.” Kerry adamantly denied that he would run for president.

Biden has pitched himself as a steady pair of hands and the strongest choice against Trump, a view polling suggests is shared by a large constituency of Democrats, particularly among African Americans who play a critical role in later contests. But he faces competition for moderate voters from Buttigieg, 38, who has risen from relative anonymity.

“The good news is you don’t have to choose between the best way to govern well and the best way to win big,” the former mayor told a crowd of more than 2,000 at a closing rally in Des Moines. “At a moment like this, history has taught us we cannot take the risk of meeting a fundamentally new challenge by falling back on the familiar. We can’t be afraid of moving to the future and new voices in our leadership.”

Warren, a former public school teacher and Harvard law professor, has pitched herself as an unabashed liberal with an arsenal of detailed policy proposals for “big structural change”. But in the last days of the Iowa race she has also sought to emphasize what her allies argue is her unique capacity to unite and excite Democrats from the party’s ideological factions, even as she confronts doubts that a woman can beat Trump.

“We will – we must – come together as a party and defeat Donald Trump,” Warren told voters at a gymnasium in Cedar Rapids on Saturday. “And I’ve got a plan for that.”

The Senate impeachment trial added an additional layer of uncertainty to the already unusual Iowa caucuses, pulling Sanders, Warren and Amy Klobuchar – and the long-shot Senator Michael Bennet – back to Washington in the final weeks. Republicans are poised to acquit Trump on Wednesday, leaving the fate of the presidency in the hands of the Democrats running to defeat him.

Q&A Why are the Iowa caucuses important? Show Hide On 3 February, voters in the midwestern state of Iowa will kick off the long process that will eventually choose the Democratic party’s presidential nominee, who will take on Donald Trump in November's US election. The primaries and caucuses are a series of contests, in all 50 US states plus Washington DC and outlying territories, by which each party selects its presidential nominee. Iowa is extremely influential in US elections because, since 1972, it has voted first. After months of campaigning, this will be the first chance to see what support each of the presidential candidates actually have among voters. Winning Iowa matters because it can give candidates a huge boost in momentum and name recognition before the other states cast their votes. Underdogs can triumph, and frontrunners can fall. Since 2000, every Democratic winner of the Iowa caucuses has gone on to win the party’s nomination. However, Iowa only has a population of around three million people, who are 90% white, which has prompted criticism that its influence in US elections is outsized.

“We better not screw this up,” Klobuchar, the senator from Minnesota who has staked her candidacy on a strong finish in Iowa, told supporters on Saturday.

If Klobuchar fails to reach the 15% viability threshold, her supporters could play a decisive role. The same applies for the tech entrepreneur Andrew Yang, who has predicted that he will “shock” the nation.

The former New York mayor and billionaire Michael Bloomberg is not competing in Iowa, having spent more than $100m on a gamble that he will win big in later contests. Trump has fixated on the Bloomberg and on Sunday their campaigns aired dueling TV ads during the Super Bowl.

Republican caucuses will also take place on Monday night, but as Trump faces no serious challengers all eyes will be on Democrats. White House officials, cabinet secretaries, members of Congress and Christian evangelicals will be in the state on Monday to offer voters a stark reminder of who and what the Democratic candidate will be up against.

“This will be the strongest, best-funded and most organized presidential campaign in history,” Brad Parscale, Trump 2020 campaign manager, said last week. “We are putting the Democrats on notice: good luck trying to keep up with this formidable re-election machine.”

Additional reporting: David Smith in Des Moines.