As established in the Constitution, the American military serves a civilian government. But that could quickly change, as I describe below.
Most of us Americans have faith that the armed forces will not serve as the enforcement arm of a dictatorship. What this means is: (1) The military as a whole will not support an attempted Republican dictatorship. The current military leadership took steps to restrain the possible abuse of military power, including nuclear weapons, by former president Trump in his final, unstable days in office. (2) Not all military personnel will support a Republican dictatorship. In fact, it is likely that most will not. We all know of individual members of the military who serve America, not a political party.
But there could still be a military coup not acting on its own but supporting the civilian attempt to establish Republican single-party rule. There will be enough military personnel who will support Trump to make the coup successful. They, the extremists, are well organized; when they act, they will leave the freedom-loving members of the military reeling with confusion and unable to prevent the coup.
We have known for months that the internal security of the US military has been weak, leaving it open to infiltration by criminals or extremists. This article describes the disappearance of thousands of weapons from the US military.
While most military personnel are not extremists, there are enough of them that, in late December, the Pentagon announced an initiative to investigate right-wing extremism in the military.
This military coup will leave America vulnerable to Russian and/or Chinese aggression.
This is the evolutionary perspective: Throughout human history and prehistory, the organized forces of power have predominated over the less-organized forces of peace. Except for brief moments in world history, as exemplified by the United States, the United Nations, and the European Union. I fear we are about to lose the first.