Democratic presidential candidate Senator Bernie Sanders holds only a slight lead over former vice president Joe Biden. — AFP/VNA Photo

IOWA CITY — Democratic candidates darted across Iowa on Sunday delivering their closing arguments to any and all who would listen, a day before the state's nominating vote that officially starts the US presidential election season.

Iowa, a largely rural state of three million people, has traditionally served as a vital launching point - or burial ground - for presidential hopefuls.

"This is the most consequential election, certainly in the modern history of this country... and it all begins tomorrow night," Senator Bernie Sanders, the leading progressive in the race, told invigorated supporters at a meet-and-greet event in Iowa City.

Similar scenes played out across the snowy state this weekend as most of the 11 remaining candidates in the race made their final push to convince undecided voters.

But Monday's caucuses have created an air of suspense with no clear frontrunner. Several hopefuls look to strike gold here and take their winning ways into the next contest, in New Hampshire on February 11.

Leftist Sanders holds only a narrow lead over moderate former vice president Joe Biden. Former South Bend, Indiana mayor Pete Buttigieg and Senator Elizabeth Warren are just a few points back.

Three of the leading candidates seized on a brief break from their duties as jurors in President Donald Trump's Senate impeachment trial to barnstorm Iowa before Monday's caucuses.

The senators - self-styled democratic socialist Sanders, progressive Warren and pragmatist Amy Klobuchar - each hosted multiple events on Sunday.

Saturday had been equally hectic.

The impeachment trial - only the third in history of a US president - created an unprecedented situation by limiting the senators' ability to campaign in Iowa ahead of the vote.

Sanders, Warren and Klobuchar must return to Washington on Monday, along with Senator Michael Bennet who trails badly in the polls, for the trial's resumption.

Senate leaders have scheduled a Wednesday vote that appears virtually certain to end in Trump's acquittal on charges of abuse of power and obstruction of Congress. — AFP