History tells us that it's more complicated.

In the Russian revolution the Tsar sent his soldiers to stop the Bolsheviks and it turned them against him. Soldiers don't like being told to kill their own people, even when they're in open revolt. Race makes this more complicated, but in a lot of different ways that are hard to predict. I'd expect desertions (and, eventually, fraggings) if Trump actually ordered the troops to open fire.