Biden insisted he had a "good night" in Iowa even as he trailed the top moderate candidate, former Mayor Pete Buttigieg of South Bend, Indiana, and the leading progressive, Bernie Sanders, according to initial returns from 62 per cent of precincts.

The results followed 24 hours of chaos as technical issues marred the contest, forcing state officials to apologize and raising questions about Iowa's traditional place atop the presidential primary calendar.

The appearance in front of around 500 people gave a first glimpse of what she may look like as a 2020 candidate.