Keep in mind that attempting to assassinate a president in itself is fairly rare. That being said, and conceding that he was not a founding father, Andrew Jackson was subject to an assassination attempt that failed due to the would-be assassin's pistol misfiring. Jackson had to be dragged off his attacker because they were afraid he would kill him before he could be arrested and tried.

You have to realize that the federal government used to have mush less power than it does now and people were much more beholden to their states' governments. Also, as the country expanded you were largely free to do whatever you wanted, laws or no, just based on the impracticality of trying to enforce said laws. If the federal government tried to impose its will on you, you had the complete ability to tell them to pound sand. Obviously this would not be the case in more urban areas.

Unless you were a population that the government had a vested interest in oppressing (e.g. the Indians) you could go your entire life without seeing any evidence of a federal government outside of the postal service.

If the founding fathers faced a perceived lesser threat of assassination it would have to be because people just didn't care enough to kill them.