I don't follow, why is this a must?
As an aside the rest of your post seems to assume that someone needs to eventually take power ala the Emperor in Star Wars. While that could be a threat to liberty the more likely scenario and the one I believe the Founders were thinking of is a slow encroachment on rights and freedoms from the federal government. I think they believed just the threat of a mass armed citizen revolt would hopefully ever keep this from occurring. I don't think they counted on the complacent couch potato society we've become.
As long as citizens are actively involved in democracy and vote for polices and politicians who will act in their best interest, and the best interests of the country and world as a whole, I see no real threat of this experiment failing. The danger is when voters become so disillusioned with or disbelieving in the validity of the system that they either don't vote, cast "protest" votes, or vote for candidates who they know won't help them, but who promise to at least hurt other people, or worse, promise to tear the system down, that the systematic checks come under stress and the experiment could be threatened.
I mean you guys have voted Trump in and half the country prefers simple lies to complicated reality. You are certainly doing alright on the despotism movement. Still a long way to go, but the track is right.