"Know for sure"? What does that even mean and where did I claim absolute surety? I said it was clear and non-controversial. Non-controversial in this context means not unexpected.
Non-controversial doesn't mean unexpected. It means that there is no controversy over it. The discussion about it here disproves that claim.
And you made a categorical claim that Bernie
can't win, not something weaker like "he is less likely to win than Biden". I expect a certain degree of certainty when somebody makes such a categorical claim.
Once again, for anyone who actually understands American politics, the fact that he is Jewish--and comes across as a "New York Jew" in particular--is a serious problem across ALL demographics, regardless of party affiliation and that's just right out of the gate, not accounting for his policy proposals. That means that there is going to be--not might be, but already exists--a certain percentage of Democrats that will simply not vote for him.
Same goes for Obama (black) and Hillary (a woman). Same went for Kennedy (Catholic). Should we only run white Anglo-Saxon Protestant men in perpetuity because some fraction of voters might not like X?
This is precisely why Putin targeted primarily minorities in order to suppress their vote.
Russian propaganda stoking #BLM discontent was a stroke of evil genius, but I do not see how it hurts only Sanders.
Hence, why, once again, among people who understand American politics, it is both clear and non-controversial to state that he can't beat Trump.
Because he is Jewish? Really? In 2008 you probably made a similar argument about how Obama "can't beat" WASPy McCain.
At most you are arguing that his ethnoreligious affiliation would make it harder for him to win than say Biden. That may or may not be true (I think his ideology is a much bigger hurdle than ethnicity or religion) but it doesn't translate into impossibility. And your analysis is directly contradicted by
head-to-head polling, which shows Bernie doing comparably or better against Trump than other front-runners.
Once again, he could NOT beat Hillary.
And yet HE DID beat Hillary. Says a lot about your assessment of what is possible or not.

[Koyaanisqatsi, ca. 2020, colorized]
Do you not understand what a popular vote measures? It's right there in the title.
Yes. I also understand what it doesn't measure. Namely, it doesn't measure WHO WON THE ELECTION. You need the ELECTORAL VOTE for that.