NBC did put the same question to respondents in February 2019 and 29% had "some reservations" and 43% were "very uncomfortable" for a total of 72%. In October 2015, and 25% had "some reservations" and 45% were "very uncomfortable" for a total of 70%. Among registered Democrats in the Feb 2020 poll, 53% said that they were "enthusiastic (16%)" or "comfortable (37%)" with a socialist candidate. In Feb 2019, 47% said that they were "enthusiastic (10%)" or "comfortable (37%)" with a socialist candidate.
A different picture emerges if one looks at the individual proposals of the "socialist" Bernie Sanders. A CNBC poll of all Americans, whether registered to vote or not, showed strong support for the individual proposals that the "socialist" Bernie Sanders makes. Goran Lazarevski makes a strong argument that "centrist" candidates like Biden, Buttigieg, and Bloomberg are not necessarily the most electable.
It doesn't matter who the Democrats nominate. The right will label them as "socialist." It is more important to have a candidate with proposals that are at the center of peoples lives rather than a mythical center. A new Yale study shows that Medicare for All would save money and lives.