Just as they knew the Constitution was inadequate for any non-moral people, they knew that it wouldn’t restrain a determined tyrant.
They made the assumption of moral people in the country and in office.
For all of Hamilton’s genius (and he was the genius of the founding fathers) he never believed that a corrupt Democrat party led by Jefferson, Madison and Burr would be able to rule in spite of the Constitution. No one was more into realpolitik than he but he was a rank idealist when it came to the forces he faced within this nation.