Could a single general lead a hostile take over?
Rome vs. United States
Rome was once a republic governed by senators who controlled the levers of power. However, the late 1st century B.C.E. Rome underwent a massive governmental change. To spearhead this change was Julius Caesar (July 12, 100 BC to March 15, 44 BC) https://www.biography.com/people/julius-caesar-9192504. Julius Caesar was a Roman General with a spectacular military career. He was beloved by his troops, the common people, and was even criticized by Roman Nobility for fraternizing with the commoner too often. Furthermore, his leadership and military prowess enabled Caesar to transform Rome from a republic into an Empire.
Today we ask if the U.S. military could pull off something similar
Could the United States be transformed into an Empire by a large rogue element of the military? The answer is possibly. During a government shutdown service men and women are forced to carry forward with their missions without pay. Military life is already stressful and performing the duties with no pay brings a serious downturn to morale. But morale alone is hardly enough reason for a rogue element to arise and overthrow the government. However, given certain conditions a new form of government could eventually be instituted. For instance, nationwide Martial Law would chuck our civil liberties into a melting pot of steel, our principles, our Constitution, our way of governance at the mercy of the mold. There may be a new way of life under empirical rule once the molten metal cooled, and that way would be given to us by the chain of command.
Service members must obey the orders appointed over them or face harsh punishment, and in extreme circumstances even death. When given an order an individual may not agree with they will always be faced with an ultimatum. This fact can bend the military to carry out the will of negative and unjust causes. Imagine our country with an 8 o'clock curfew, tanks every other block, barricade blocking roads, and a base of operations at the local courthouse. Given the current political climate, it would not take much to trigger a future like this one. Add relentless nationwide protests, daily riots and looting by mobs numbering in the hundreds of thousands, coupled with a political leadership hesitant to govern, and the obvious choice to consider would be unleashing the military on the American populous. However, this decision could fracture portions of the military leaving the door open for Generals and Admirals to collaborate thereby guiding their troops on a path against the political leadership.
Civil War
In the Roman civil war, Caesar would direct his troops against the forces of Pompey. Pompey being on the side of the Senate was the last hope for the Republic. Eventually, Pompey would lose the "Battle of Pharsalus", leaving Caesar as the clear victor. However, there was a small holdout of soldiers still loyal to the Senate, but Caesar would make quick work of this group as well. Nevertheless, Caesar triggered this civil war by bringing his army across the Rubicon River. At the time it was considered treason for Generals to bring a standing army across the Rubicon. This action officially made Caesar an enemy of the state. In comparison, it would resemble an American General randomly deciding to march a few battalions onto the White House lawn. Today "Crossing the Rubicon" means making an unwavering and irreversible commitment to something.
So, is there any leadership among the U.S. ranks willing to follow in the steps of Caesar? It's highly unlikely, but if the order were given to in-state national Martial Law by an elected official, all bets are off. The divide would be very similar to the one in the Roman civil war. Also, many people in the military would wish to preserve the constitution and old traditions of the United States, but the main force and traction would likely side with the elected officials. The military is at the whim of elected representatives and if their intentions are devious so too are the military's.