The founders did anticipate direct democracy, the two-party system, and demagoguery. These were much discussed. They weren’t able to provide perfectly for these eventualities, which also was well understood at the time.

The constitution clearly doesn’t allow a president to be removed from office by a prosecution, but it just as clearly doesn’t offer any immunity to a prosecution for presidents and not to mention ex-presidents. There’s never been a presidency, including Donny’s, where a criminal charge was even contemplated that would have impinged on a president’s legitimate duties.