To see how the Bernie people are responding to the debate, I checked the Twitter feeds of several visible progressives (Michael Tracey, Jordan Chariton, Nomiki Konst). One major objection all of them had was about Trump's law-and-order theme, not on pragmatic grounds, and not in a yawning or glib dismissive tone of voice. For them it's one of those moralistic crusade issues that provokes a visceral emotional reaction.
Back during the anti-globalization movement of the early 2000s, I was anti-authoritarian like many other students involved. But kneejerk "question authority" feelings should be outgrown once you're out of college, and these progressives are about 30 or older. They're probably representative of the rest of Bernie's followers, who were largely under 40.
Pushing an issue that resonates primarily with young adults, and that turns off older adults (over 30 or 40), is strategic suicide. Especially once the crime rate enters its upward phase of the cycle again, or when there's a rising threat of terrorism. And while cops may not garner the level of trust that the military does, law enforcement is still up there compared to most other institutions (courts, media, churches, etc.).
If anything, ordinary Americans don't trust the police to the extent that they hang back and cover their ass, rather than get in the way of criminals when crimes are being committed, or aggressively prevent them. Normal people would like a stronger police force -- not an even weaker one than the apathetic kind that we already have.
Police who refrain from targeting the worst threats and offenders are apathetic and weak, no matter if they occasionally go after a more harmless target, just to give the impression that they're doing serious police work.
When people demand stronger police, they don't mean more heavy-handed treatment of skateboarding teenagers at the shopping center -- they mean a force that would prevent the Charlotte riots from ever beginning, including not allowing them to mill about in the open streets after dark, which gives them the feeling of owning the entire territory and emboldens them to break apartment building windows, loot stores, bust up cars, and start fires in trash cans.
Working and lower-middle-class whites are particularly suspicious of the anti-police view among progressives, which they take to be elitist entitlement -- "I went to college, so how dare the pigs ask to see my ID for anything." That conclusion is hard to shake when the progressive in question sounds like they're still stuck in their adolescent "smash authority" phase.
Now, just because a goal is strategic suicide for the broader plans that a movement has, does not mean they will simply put it on the back burner. If it has moralistic intensity for them, it's not negotiable, and when pressed they will vigorously defend its importance.
Progressives are even more reluctant to let this issue go because it's their only foot in the door to minorities, who otherwise have little interest in progressive causes (witness Bernie's epic failures wherever the non-white population was common). The progs know you can't win a liberal or Democrat constituency without winning over minorities, so they have no choice but to keep focusing on the anti-police issue, given their aversion to identity politics.
Remember, though, that black people and progressive whites view the anti-police issue in two different ways: for blacks it is an anti-white stance, for progressives it is anti-authoritarian. No matter which angle is emphasized, it will turn off white working-class people, who are a far larger constituency in Democrat politics.
Caught between a rock and a hard place on which coalition member to alienate less, the anti-police progressives seem to be doomed to marginal status for the near future. The same can be said, for that matter, about the hardcore libertarians on the Republican / conservative side.
With the old Clinton / Obama coalition coming apart at the seams, it's the Bernie people who are going to determine where the Democrats go in the next several election cycles. If they can't let go of their moralistic anti-police stance, they may doom themselves to McGovern / Mondale status as the law-and-order Republicans akin to Nixon and Reagan take over again.
Notice that this time, though, the Left will not have as many cards to play against Trump -- he has totally made anti-globalization his own specialty, in both trade and foreign policy, not to mention his push to root out corruption, especially by big banks and other big industries.
The Bernie people could try to win over the populist voters with their programs about single-payer health care and debt forgiveness for student loans. But Trump is not adamantly opposed to either idea qualitatively, although he might not go quite that far in degree.
Really the only two big issues that will remain sharp distinctions between the Bernie side and the Trump side in our new populist era, are climate change / taxing carbon and law-and-order / gun control. No amount of progressive campaigning will convince working-class whites that these two themes are better solved by the Bernie side, which will come off as trying to push for elite concerns that the middle and lower classes don't care much about, and if they do, it's more in the pro-Trump direction.
Progressives also favor amnesty, but once Trump deports those who would get it, it will cease to be an issue. Bernie, Nader, etc. do not want high levels of immigration because they know it's just a scheme by the wealthy business owners to cut labor costs and pocket the difference in profits. We're going to have a big fat beautiful wall, too, a one-time accomplishment like the deportations that will have long-lasting effects. The progs can simply enjoy the benefits without having to "own" the means that achieved them.
If this "40 years in the wilderness" sounds unrealistic, just think of how self-marginalizing the Right behaved for decades over abortion. It was not pragmatic, let's try to cut down the number, etc. -- it was a contest to see who could hold more extreme views on how few exceptions they would permit, and anyone who permitted more exceptions was moralistically shunned. It's not beyond belief that the Left will evolve toward marginality over policing / gun control -- probably not over climate change, which is too abstract to really turn someone off, compared to something as visceral as violence, social chaos, and protection from it.