I mean, I think they’d have considered a civil war less than 100 years after the founding of the country to be a pretty good indication of failure.

As for the modern world, they explicitly talk about trying to design a system so that a tyrant doesn’t become president. All the supposed checks and balances that were supposed to prevent that turned out to be as effective as wet tissue paper. The founders also cared a lot about the president not being corrupt, and drafted the emoluments clause(s) to prevent that, and Trump has just completely ignored those clauses. I think they’d have been pretty upset about that, and wondering why the law of the land was just being ignored.