The Democratic preference for nominating a candidate who can win next November is particularly strong. A year before the presidential elections in 2004, 2008, and 2016, CBS News/The New York Times Polls found Democratic primary voters far more interested in supporting candidates who agreed with them on issues than candidates who could win. In those three years, between 62% and 73% of Democratic voters said they preferred a candidate that agreed with them on the issues, while 36% was the highest percentage saying it was more important to find a candidate who could win [In 2015, Republican voters said the same thing, prioritizing issue agreement over electability, 60% to 35%.]
This year, liberals and older Democratic voters are especially likely to prioritize winning over policy positions. African-Americans are far more closely divided on what is more important.