Joe Biden is barely clinging to front-runner status and Bernie Sanders has fallen sharply as Democratic voters give new attention to Kamala Harris and Elizabeth Warren after their strong debate performances.

Biden remains at the head of the pack of Democratic presidential contenders -- though barely -- in a Quinnipiac University national poll released Tuesday. The former vice president had support from 22 per cent followed by Harris with 20 per cent, a result within the margin of error. Warren had 14 per cent support and Sanders was at 13 per cent in the poll conducted June 28 - July 1.

That’s an 8 percentage-point drop for Biden since Quinnipiac’s June 11 poll and it represents a major boost for Harris, who had support from 7 per cent in the early survey. Sanders also slid from 19 per cent while Warren’s standing was little changed.

It’s the second poll since last week’s Democratic debate showing Biden’s front-runner status put in peril. A CNN poll released Monday found Biden’s lead over the field had shrunk by 10 points as Harris and Warren got significant bumps in support.