The US is not particularly resilient. FDR got 3 terms and would have probably got a 4th, GWB pre-Katrina had enough political capital to abolish the 2-terms limit had he dared to do so... GWB also widely abused his presidential powers, and never faced any consequences. Trump had to resort to violence simply because he was too weak.
FDR did not have to do any maneuvering whatsoever to get his 4 terms - Grant had already run for a 3rd before him, as had Teddy Roosevelt. There was no rule against it an the people wanted him in power, so he stayed in power. Similarly, GWB didn't run for a third term, regardless of what he "could have" done. Neither of your examples are very strong here.
The point is that the US system, by itself, has no really-strong guarantees against tyrannical rule. The overall political culture of US voters is what produced the results they got, not the system by itself.
This is true in reverse too: for example, Italians have been tinkering with their electoral system for 30 years now, but one way or the other they continue to change their rulers almost every year. Systems can make some mechanisms more or less awkward, but in the end it's the shared political norms that make the real difference.
You can read a lot of the old discussions between the founders Madison, Hamilton, etc. and the type of abuse they were worried about and how they thought the structures they put in place would reduce risk.
There is also an element of culture required among the population too that’s necessary.
> “I have already intimated to you the danger of parties in the state, with particular reference to the founding of them on geographical discriminations. Let me now take a more comprehensive view, and warn you in the most solemn manner against the baneful effects of the spirit of party, generally.
“This spirit, unfortunately, is inseparable from our nature, having its root in the strongest passions of the human mind. It exists under different shapes in all governments, more or less stifled, controlled, or repressed; but, in those of the popular form, it is seen in its greatest rankness, and is truly their worst enemy.
“The alternate domination of one faction over another, sharpened by the spirit of revenge, natural to party dissension, which in different ages and countries has perpetrated the most horrid enormities, is itself a frightful despotism. But this leads at length to a more formal and permanent despotism. The disorders and miseries, which result, gradually incline the minds of men to seek security and repose in the absolute power of an individual; and sooner or later the chief of some prevailing faction, more able or more fortunate than his competitors, turns this disposition to the purposes of his own elevation, on the ruins of Public Liberty.”
