His opponent also failed to outperform Trump – in other words, there were fewer total votes cast for that race than there were for President, i.e. some people just voted for President and left the rest of the ballot blank. As for percentages, Sanders was within a percent of Harris, which sounds like statistical noise to me.
On top of that, what matters to this conversation is how people in states Trump won would behave, not how people in Vermont would behave. Vermont is less unequal and less impoverished than most other US states, so there’s plenty of reason to think that his platform would be even more popular in places other than Vermont, if those voters had the chance to actually hear about it.
some people just voted for President and left the rest of the ballot blank
Yes, that’s exactly what they did. They intentionally left a blank next to Sanders’s name.
They sure didn’t do that in Wisconsin. In Wisconsin, voters made sure to vote for Tammy Baldwin. In fact, many people voted for Tammy and left the presidency blank, or even voted for Trump. And Wisconsin is equally un-impoverished and even less unequal than Vermont.
Likewise Ruben Gallego and Elissa Slotkin proved their ability to bring in people who didn’t want to vote for Harris. Whereas Sanders failed. The future of the party lies with those who deliver actual results.
Sanders supporters keep making excuses for him, but the fact is that his supposed ability to bring in non-Democrats has never been demonstrated in a real election. It’s just wishful thinking, exactly the same as “There’s plenty of reason to think that Kamala will be popular with white women”.