I have always felt the greatest danger posed by the Trump presidency is the precedents and standards set which could easily be taken advantage of by someone in the future who was far more cunning and treacherous than Trump appears to be. History has shown us that once lines are crossed by a president it is extremely difficult to ever restore the old rules.
The new leader can always say, “Trump did it, so I can too.” Before you know it, things that used to be largely unthinkable are happening without even provoking much of a reaction (kind of like Trump saying that it is sort of “treasonous” not to applaud him in a speech to Congress).
That is exactly how a country can be rapidly, fundamentally transformed. Once the next Trump (on steroids) gets into the Oval Office, the leap from military parades for the personal pleasure of a king-like executive, to that person invoking martial law, is suddenly not so large at all.