Here’s a good article that gets at the real issues with predicting how strong a general election candidate Bernie Sanders would be. It’s different because it gets down into the specifics with real data. Indeed, what is particularly strong about it is that much of what it says people on both sides of the intra-Democratic debate agree on. (We’ll get to that in a moment.)
As I’ve argued, I don’t think you can say Sanders is unelectable or some kind of sure loser when a year’s worth of public polls show him beating President Trump. Current polls show Sanders and Biden both beating Trump by comparable margins. Until recently, they showed Biden doing somewhat better. But compared to all the other candidates they ran relatively similar margins against the incumbent President.
This article gets into the fact that even though the toplines are similar, they’re made up of significantly different coalitions.