Well, it took a lot of people by surprise that our famed checks and balances turned out to be toothless. Schoolhouse Rock sure didn't teach me that when other branches of government try to tell the executive branch to cut it out, they can just reply "no lol get bent".
The fatal mistake I see people repeatedly making is that it isn't about the system or checks and balances or whatever. It's about the people. The US had a deep bench of mostly reasonable leaders that mostly respected ideas like checks and balances or conflicts of interest.
Those people are mostly gone now. Our society used to elevate people like that, but it just doesn't now.