Our governmental type was an experiment. I'd guess a lot of the FFs had serious doubts it could last, they wrote as much, some of them.
The FFs feared pure democracy about as much as monarchy, and maybe more. Nothing like this had ever been attempted, not even in Greece back when. And it was unique in the world at the time. The European monarchies no doubt sneered at it, and were thankful it was "over here". They reacted rather strongly when France started a kind of republic of course. The French attempt obviously failed quickly, and badly.
They are on the Fifth Republic now (and not doing all that great either).
I think we're still in the experiment phase, and it's interesting we've lasted this long, but at some point, voters know they can elect politicians who will pay them off, and that happened a while ago, hence our burgeoning national debt.