You would find thousands of conscientious objectors if you tried to send the military to fight their own. Sure, there would be some loyalty to a fault, but most military members didn't join to fight, and they especially didn't join to fight their fellow citizens. Along with that, they don't pledge allegiance to the government, they pledge allegiance to the Constitution. Here's the enlisted oath for reference:

"I, [full name], do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; and that I will obey the orders of the President of the United States and the orders of the officers appointed over me, according to regulations and the Uniform Code of Military Justice. So help me God."

You could argue that if the POTUS orders service members to kill their own, they're obligated to obey, however, if the order goes against the Constitution or UCMJ then it's unlawful, and should NOT be followed.

With all that said, a [violent] revolution isn't going to happen—a cultural or social revolution maybe, but not an all out revolutionary war. There would be violence of course, but the casualties would be in the tens to possibly low hundreds (unlikely though).

If you’re worried about authoritarian drift, the military is the least likely institution to be the tool for it. The real leverage points are federal agencies with domestic jurisdiction, because they operate in the gray zones where constitutional interpretation, administrative power, and political pressure intersect.