A broad field of US Democratic presidential candidates have delivered their sales pitches to party leaders in Iowa, touting their ability to engage voters, defeat Donald Trump and deliver on longtime party goals such as universal healthcare.

The 19 Democrats running for 2020 had five minutes each to sum up their case for the presidency.

Most agreed on the problems, including climate change, improving public education and easing pay and wealth inequality.

“Now is not the time to be polite … Now it’s time to fight like hell,” US Senator Kirsten Gillibrand told the 1400 guests at the the state party’s Hall of Fame dinner.

The dinner came one day after a poll showed former US Vice President Joe Biden leading the pack in Iowa.

US Senators Bernie Sanders and Elizabeth Warren, along with South BendIndiana Mayor Pete Buttigieg, were bunched closely in a fight for second place in the poll.

Senator Sanders took what seemed to be a veiled swipe at Mr.Biden, who wasn’t present.

“I understand there are some well-intentioned Democrats and candidates who believe the best way forward is a middle-ground strategy that antagonises no one, that stands up to nobody and that changes nothing,” the Senator said.

“In my view, that approach is not just bad public policy, but it is a failed political strategy that I fear would end up with the re-election of Donald Trump.”

Meanwhile former Colorado Governor John Hickenlooper took aim at Sanders’ democratic socialist agenda and said it could be a stumbling block to defeating Mr Trump in 2020.

“We must present a bold vision for the future, but we also must acknowledge that the most effective charge Republicans can level against us is ‘socialism,’” he said.

Former US Representative John Delaney said Democrats should be a “big-tent” party that appealed to progressives, moderates, independents and disaffected Republicans.

“If we become that party, we’re going to win every election. And more importantly, we’ll be able to govern,” he said.