Dems. According to Gallup, Dems = 29%, Republicans = 28% and Independents = 40%.
The poll in the OP had a sample of Dem=38% (+9%) Republicans =27% (-1%) and independents=35% (-5).
What does this tell someone reading the poll results? It would generally indicate a Democrat bias of +10% in the poll.
A 'proper' poll of registered voters would have a sample that more closely reflected the national party affiliation.
https://news.gallup.com/poll/15370/party-affiliation.aspx