That's among Dems. You are discounting independents, nonvoters and Trump crossovers. Trump marketed himself as a populist in 2016 (he wasn't of course) but Bernie will draw from that tent. Bernie Sanders is the most popular political figure in the country. The centerleft has been bred to blame/hate Sanders for Trump, but most normal people know that this is a red herring.
Most Democrats are not going to vote for Trump over Bernie, or stay home because Bernie isn't a registered D. Those are D votes no matter what, by your own logic, since they will be "uniting to defeat a common enemy". What is the word 'democrat' supposed to stand for anyway, if not a democratic process? If you want a safe and bloodless primary then let the party elites handpick someone in a backroom and skip the theater. They already tried a triangulating centrist, got their way, boosted Trump in the primaries and then ####### lost to him. The orange cheeto dust is on their hands, not Bernie's. Sanders, by contrast, may have actually won the 2016 election. It is time for centrists to get out of the way and see how a real left opposition party does.
For what it's worth, I don't like Bernie Sanders, but for different reasons than you don't. I think he's a liberal imperialist, waffles on Israel and is a total coward on BDS, shouldn't have humored this Russia garbage (which will be weaponized against him just like Gabbard, Corbyn, Stein etc., watch), has the wrong diagnosis for the symptoms, super old, etc. But there is no denying that he's an impactful figure in politics. From his support for labor against Amazon, teachers' strikes, the new push for M4A, the Yemen resolution passed in the Senate, you really can't discount that he's been an important factor in national politics. Look at
this. It's a searing image.
What I find incredible is that people still blame Sanders for dividing the party, and not supporting Clinton hard enough. It was the DNC that divided the party by favoring one candidate in what should have been an open primary process. If we're talking about divisive, maybe we should talk about the DNC leadership that got ####canned for running a biased primary, or the guy that wanted to "put a fork" in Bernie's latino support, who now, naturally, runs the DNC.
He could have ripped the DNC apart for what they did to him, and should have. He displayed total cowardice letting it slide and endorsing Clinton. They should have thanked their lucky stars that Sanders fell in line. Enough with the Bernie/Russia blaming crap, and enough with the lame excuses for why the DNC/Hillary/CAP brand failed. Nope. It's not gonna happen. Not this time.