Mr. Esper’s downfall had been expected for months, after he took the rare step in June of disagreeing publicly with Mr. Trump and saying that active-duty military troops should not be sent to control the wave of protests in American cities. The president, who had threatened to use the Insurrection Act to do exactly that, was furious, officials said.
There was a moment there where the use of the military in major cities was contemplated and could have occurred. When Trump marched with his generals and defense secretary past protesters who had just been teargassed for a photo-op at a church he never attends. Don't forget that Trump kept coddling and buddying up to the military by putting generals in charge in civilian positions and dumping lots of extra billions into the military complex. Fortunately he never succeeded in buying off their loyalty.
Who knows how such an alternate reality goes, but the protests might have ramped up in reaction to such a blatant un-American approach to policing. A military crackdown in US cities might have caused even greater division and helped Trump push lawnorder and overshadowed the Virus somewhat. There almost certainly would have been more violence on both sides. Hell, even more violence by armed Trump supporters at BLM protests could have sparked Trump to bring in the military.
As it was, Trump used unmarked Homeland security goons in Portland but it never became widespread or accepted. But if Trump had invoked the Insurrection Act and the military was deployed to keep order/crack heads in US cities, this could have set the stage for Trump not only contesting the election result but claiming victory and having the military back him up. Just saying this was possible if Trump had successfully put the military into the midst of US cities and the election campaign.
It might sound far-fetched but only because it didn't happen. Trump never went full fascist or got the military fully on board with his personality cult. But we also weren't that far from such a scenario being played out or tried.