The US Democratic Party’s leading presidential candidates have sparred over Iraq, war and foreign policy in the final debate showdown before primary voting begins.

Progressive Senator Bernie Sanders drew an immediate contrast on Tuesday with establishment favourite Joe Biden by noting that Sanders aggressively fought a 2002 measure to authorise military action against Iraq.

Mr Sanders called the Iraqi invasion “the worst foreign policy blunder in the modern history of this country”.

Mr Biden acknowledged that his 2002 vote was “a mistake,” but highlighted his role in the Obama administration helping to draw down the US military presence in the region.

Just six candidates gathered in Des Moines, each eager to seize a dose of final-days momentum on national television before Iowa’s February 3 caucuses.

It was not the focus in the debate’s earliest moments, but a sudden “he-said, she-said” dispute over gender involving two longtime allies, Bernie Sanders and Elizabeth Warren, loomed over the event.

Specifically, Ms Warren charged publicly on the eve of the debate that Sanders told her during a private 2018 meeting that he didn’t think a woman could defeat Trump, a claim tinged with sexism that Sanders vigorously denied.

Amid an immediate uproar on the left, there were signs that both candidates wanted to de-escalate the situation.

The feuding was likely to expand to include nearly every candidate on stage by night’s end.

Mr Trump, campaigning in neighbouring Wisconsin just as Democrats took the debate stage, tried to encourage the feud between Sanders and Warren from afar.

Bernie Sander’s volunteers are trashing Elizabeth “Pocahontus” Warren. Everybody knows her campaign is dead and want her potential voters. Mini Mike B is also trying, but getting tiny crowds which are all leaving fast. Elizabeth is very angry at Bernie. Do I see a feud brewing?

— Donald J. Trump (@realDonaldTrump) January 13, 2020

“She said that Bernie stated strongly that a woman can’t win. I don’t believe that Bernie said that, I really don’t. It’s not the kind of thing Bernie would say,” Mr Trump said.

-AP