The three candidates are bunched together, each receiving about the same amount of support (Sanders 20%, Warren 20% and Biden 19%) from registered Democrats and Democratic-leaning independent voters.

They're followed by California Sen. Kamala Harris (8%), New Jersey Sen. Cory Booker (4%), South Bend, Indiana, Mayor Pete Buttigieg (4%), businessman Andrew Yang (3%), former Housing and Urban Development Secretary Julián Castro (2%), former Rep. Beto O'Rourke (2%) and author Marianne Williamson (2%). All other candidates received 1% or less in the poll.

Since Monmouth's June poll, Sanders and Warren have gained slightly (up 6 and 5 percentage points), while Biden has lost significant support (down 13 points).

CNN poll conducted by SSRS, out last week, found Biden with 29% support, while Sanders and Warren were lower (15% and 14%, respectively).

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