Democratic presidential hopeful Bernie Sanders has said his judgement is as important as the experience of his rival Hillary Clinton.
During their last TV debate in Iowa a week before the selection process begins, he also admitted that he would raise taxes if he won, adding some families would still be better off.
Mrs Clinton once had a comfortable opinion poll lead in the state.
The pair are now running neck-and-neck. Martin O’Malley is a distant third.
Profile: Hillary Clinton
Profile: Bernie Sanders
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Poetry or prose?
CNN’s televised debate in Des Moines, Iowa, could be summarised as pragmatism versus passion, reports the BBC’s Laura Bicker.
During the event, at which the three candidates appeared separately, Hillary Clinton praised the “poetry” of Senator Sanders’s campaign but said the country was “governed in prose”.
Her critics “throw all this stuff at me – and I’m still standing”, she said.
The Vermont senator, who has energised young voters with his call for a political revolution, repeated his pledge to “take on the greed of corporate America”.
He contrasted his own commitment to a “Medicare-for-all” programme and free public university tuition to Mrs Clinton’s vote to authorise the Iraq war and early support for the controversial Canada to Texas Keystone pipeline.
Mrs Clinton highlighted her “40-year record in going after inequality” and suggested Mr Sanders was ill-equipped to face the tough challenge of being president.
She also said she was “really touched and gratified” to see comments from President Barack Obama in a Politico interview, in which he called her “wicked smart” and suggested Mr Sanders benefited from “the luxury of being a complete long shot”.
Mr Obama has not endorsed any candidate and the Sanders campaign has applauded his “even-handedness” throughout the campaign.
Mr O’Malley, meanwhile, was cheered when he cited climate change as the issue young Americans should be most concerned about.
He enjoined his supporters to “hold strong” and continue the struggle for the presidential ticket.