AskHistorians

Some of them were pretty well read-up on political theory and historical forms of government, which helped them conceptualize how a ~~bee~~ new government ~~my~~ could work. And some of them were seasoned 'businessmen' (some of them basically being slaveowners) or local government officials, so they had some practical leadership/management experience. But definitely not all of them.

They also had plans to periodically adjust the ~~condition~~ constitution for the growing needs of the country. But they were also very wary about foreign manipulation and domestic populism derailing the county. So they locked ~form~~ down the requirements for amendments pretty tightly. And that has arguably crimped political adaptation over the last few centuries.

Plus they didn't really anticipate the huge growth in the population or the country's future needs for the next ~~could~~ couple of centuries. But that's a hard feat to accomplish.

Edit: curse you autocorrect!