Keith, I would be glad that you are right, because I do not have any desire for the kinds of conflicts brewing now, not in the country where I live, nor anywhere. I want to be clear on one thing though, because I apparently was not:
If you look at Germany's civil war after 1918 in the aftermath of the Russian revolution and in Weimar Berlin, a free-for-all broke out in the streets between ideologically driven factions. Nothing in the US today remotely compares with this, certainly not Chicago police killing black young men as usual.
What happened in Chicago was highly unusual: a police officer was *convicted* for killing a black youth. This was a great victory for many reasons (given that police officers are almost never convicted of anything in this city). It also meant there was no reason for what people in the city widely feared would happen in the case of non-conviction, namely a major riot. In fact, the police were out everywhere in force, out of fear from higher up that one of their colleagues would be set free. Had a riot happened - a big one I mean, with fire etc - I think the federal administration would have likely found a way to make good on its oft-reiterated threats of sending the national guard and/or army into the city. Under the present polarized circumstances, such a confrontation could spin out of control, legitimizing hard-right policing and vigilanteeism as we saw in the wake of the big racialized conflicts of the late 1960s.
Social relations are very tense here, and while of course you are right that the US is a very powerful and institutionally stable country, still there are major sectors of the former industrial working classes who are very resentful about a lot of the changes that happened during the neoliberal period, and rightly so in some senses. That resentment has been stirred up in the forms of nationalism and racism and what you might call "policism" (as distinguished from militarism) and although it is quite different from what's going on in Brazil, it's also connected as part of a larger period shift, as you would seem to agree.
The US has tremendous economic and military strength, but the legitimacy of its institutions domestically is at the lowest point I have ever seen. That could be an opening for positive change, and for better or worse, it could ultimately produce a yet stronger and resilient system. Many people would like to see a more just society ready to face things like Hurricane Michael, as opposed to getting into another war or simply falling into deeper polarization and political paralysis. That desire for positive change is where all the social movements are coming from (Me Too, Black Lives Matter, Standing Rock and there will be more). But currently there is a response of intense right-wing hatred toward those movements, and to all environmental claims, and to Latin American immigration, and to Chinese economic power, and the list goes on. I am far from alone in the feeling that the old order is breaking down and the future is uncertain.
It could be just a blip, and if people mobilize in the right way, all this could in retrospect look like an important stimulus for much-needed change. But we are not there yet. Trump may not be Bolsonaro, the South Side of Chicago may not be Rocinho, and you are definitely right that this is not anywhere near civil war; but ideological shifts in the US always have far-reaching consequences, as they did after 1970s for example. And at street level, there have never been so many guns in private hands, nor such incredible aggression from increasingly militarized police. I assure you, this moment is really excruciating.