These discussions are always difficult for me to engage in, partly because so much is conflated and confused.
There are both peaceful and violent protesters. I know a non-trivial number of people that have peacefully protested police brutality in the last year, and there were no allegations of violence by these protesters. There are also indeed violent protesters, people that quote MLK regarding riots being the language of the unheard and believe this is the best option to create true change, etc. Left-wing media would have you believe that violent protesters are perhaps a trivial minority, while right-wing media would have you believe they are the problem (you can swap these views when it comes to the police violence topic). Any sort of discussion focusing on the statistics/numbers probably won't go anywhere; we can also try to come to some sort of consensus on "reliable sources", and I think we'd be hard-pressed to all agree on one (tangentially, I personally have preferred WSJ and very recently Reuters).
Anyway, I think violent protesters should be held accountable for their actions, but peaceful protesters not breaking the law should not be "caught in the crossfire". Unfortunately, peaceful protesters are, sometimes because they are in the wrong place at the wrong time, but sometimes because I don't think all law enforcement officers necessarily would differentiate. These two groups may effectively be conflated, as well... just like "good cops" and "bad cops" are by the other side. We have people following and violating the law on both sides in debatable quantities.
White nationalism and Antifa are both definitely ideologies, but how do we identify members of these groups? It's not always easy. The state I live in is considered to have some of the highest hate group participation rates in the country, but whenever members of these groups are interviewed, they deny being in a hate group. I believe Antifa itself is not really an organization, as much as some sort of umbrella term that radical left-wing groups use to protest government and police actions.
There's just a mess of groups and ideas that are too difficult to delineate, categorize, etc. Violent people do need to be held accountable, and that includes citizens and police officers. I recently saw a very clear and undeniable video of a police officer sexually assaulting a woman, and none of the many officers present did anything about it. I also tried to help a friend of a friend who was assaulted by a counter-protester during a protest while a local police officer encouraged the violence, but the "viral video" the left propagated falsified some details of the event, and I think an honest depiction would have actually been much more effective at remedying the situation. The point is, again, that so much is manipulated, conflated, confused, and used to generally mislead or persuade people towards one side or the other. We end up holding onto what we relate to, further reinforcing the views we pretty much already had. The level of emotion in our media helps, as well.
I don't think it's often that leaders can simply stop or fix a problem, especially ones as complex as some of them that have become "top-of-mind" in the past year. However, in America, the president does influence the rhetoric of the mainstream political movements. They influence the anger, the tone, and the perception of the country's citizens. They influence our idea of "how things are going". They influence the aforementioned emotion. Mastering this influence is key to being a good leader. A good supervisor chooses his words carefully and needs to think about how they will be perceived. I'm sure most people here have an example of a boss they had that was perfectly capable of creating a toxic environment. This is one of the major problems with Trump, imo. I don't actually think he's cognizant of the effect of his words, but they do definitely have a profound effect on the current angle of both political movements. One could argue (and some in this thread have certainly implied so) that a leader that doesn't raise alarm so overtly could effectively hide the problems of a country. I definitely agree with this. This is really what I see as the good side of the current administration, i.e. the cracks show a little bit more which provides more opportunity for insight.
I think that this time in America will prove to be a valuable and notable history lesson in the future, but I can't speak to exactly what that lesson will be right now.