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 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.