If stating facts about a candidate’s record feels like “poisoning the well” to you then perhaps they’re not good candidates. In any case, Hillary voters voted McCain in 2008 at a massively higher rate than Bernie voters voted Trump in 2016, yet Obama still won. Considering the fact that many Bernie voters were non-voters or Independents who only participated in the Democratic primaries specifically for him and had far less reason to support Hillary after how she cheated and insulted them, blaming his base is about as far off from reality as you can be.