I don't think Trump turned the United States into a "banana republic." It has arguably been one since its founding.
What are some of the characteristics of a "banana republic"?
Massive wealth inequality? Check.
A persecuted ethnic or religious minority? Check.
Civil War? Check.
Repeated assassinations of genuine populist leaders (Lincoln, both Kennedys, MLK)? Check.
A bloated military far in excess of the state's genuine security needs? Check.
A government more responsive to the desires of the global rich than the people? Check.
and on and on and on...
Trump emerging as a right-wing populist demagogue who gains power by distracting the people from the real sources of their pain while not actually challenging the status quo (as happens from time to time in "banana republics") is merely the latest symptom.