I'm glad you've picked this topic back up- I followed it with interest.
I'd like to propose Robespierre.
Although a product of the Revolution, his peculiarly twisted leadership poisoned any hope the Republic would flourish in any sort of liberal way.
The Terror ensured a conservative backlash & with many of the idealists executed, government was liable to fall into the hands of the opportunists.
I know I'm not being particularly brilliant by suggesting N.'s rise is a direct outcome of R.'s terror tactics.
A Danton who survived & led France may have made for a continuation of the Republic well into the 19th century.