CEDAR RAPIDS, IOWA (REUTERS) - The final countdown to the Iowa caucuses is on.

Ahead of Monday night's (Feb 3) caucuses, which kick off the state-by-state nominating process to pick United States presidential nominees, Democratic candidates are making their closing pitches in earnest around the state.

Public opinion polls show a close race among the top of the 11 contenders vying to challenge Republican President Donald Trump in November.

Senator Bernie Sanders and former vice-president Joe Biden are neck-and-neck for first place, with Senator Elizabeth Warren and former South Bend, Indiana, mayor Pete Buttigieg not far behind.

"I would call it the Super Bowl of campaigns," quipped Senator Amy Klobuchar, whose long-shot bid has strengthened in recent weeks, in a nod to the American football championship taking place on Sunday.

'BERN-CHELLA'

A confident Mr Sanders, riding high in the polls in Iowa, drew a crowd of 3,000 people last Saturday night at a star-studded event at Cedar Rapids' US Cellular Centre.

Many of the mostly young attendees who make up the 78-year-old Mr Sanders' enthusiastic base wore "Bernie" T-shirts, while others were clad in apparel of the band Vampire Weekend, arguably the true headliners of the event.

Along with a gig last Friday night in Clive that featured the folk musician Bon Iver, the weekend rally was informally dubbed "Bern-chella", after the Coachella music festival.

Mr Sanders' warm-up acts included activist and academic Cornell West, filmmaker Michael Moore and a raft of progressive politicians.

"The reason we're going to win here in Iowa, the reason we're going to win the Democratic nomination, is because we are a campaign of us, not me," Mr Sanders said, after Vampire Weekend played him onto the stage.

The campaign said the crowd was the biggest yet for any candidate in Iowa this cycle.

Some attendees Reuters interviewed were from out of state and therefore unable to caucus on Monday.

Mr Tyler Martell, 28, a teacher from Wisconsin, said he was trying to catch several of the Democratic candidates this weekend in Iowa. He said Mr Sanders' brand of Democratic socialism would be a tough sell in a general election against Mr Trump, who drew an estimated 6,000 people to the same venue in 2017, after taking office.

"I think he would be the least electable out of all them," said Mr Martell. "I'm not saying Bernie can't win, but if Democrats want a sure thing, they should go with somebody else."

IOWA TWO-STEP

The two-step Iowa caucuses can be confusing even for Americans who follow politics closely. This year, they attracted a group of European lawmakers and legislative staff who spent the weekend attending campaign events to better understand the US electoral system.

The caucuses require voters to attend a lengthy meeting in person and vote in the open by raising their hands or gathering with fellow supporters.

Caucus-goers do not just vote once. After the initial tally, supporters of any candidate who fails to register 15 per cent of the vote have the opportunity to "realign" with another contender, before a final count is conducted to determine the winner.

Ms Kerstin Lundgren, a long-time Swedish Parliament member who was waiting to see Ms Warren in Indianola, said she was impressed by how engaged Iowans - and the volunteers pouring into the state from all around the US - are in the political process.

International interest in the caucus is so high that students from around the globe are also attending. A group of about 20 students from Australia made up part of the crowd at a rally for Mr Sanders in Indianola last Saturday.

SUPER BOWL WATCH PARTIES

Some of the candidates were to cap their super-charged schedules on Sunday by joining Iowans to watch the Super Bowl.

Mr Sanders' campaign is hosting a "big game watch party" in Des Moines, while Ms Warren plans to drop by a party hosted by a liberal activist group in the same city.

Ms Klobuchar, the senator from Minnesota, will chat with football fans during the first commercial break at a bar in Johnston, Iowa. Mr Buttigieg's campaign said he planned to visit a few Des Moines-area bars during the game.

Former New York mayor Michael Bloomberg is skipping Iowa as part of his unorthodox bid, but he will show up at Super Bowl parties across the US in a multi-million-dollar commercial for his campaign set to run during the game.

Mr Trump's campaign has also purchased a Super Bowl ad.

The senators might not be able to stick around for the final score. All three are due back in Washington by late morning on Monday, when closing arguments begin in Mr Trump's impeachment trial in the Senate. Ms Warren has already said she will go back on Sunday night.