I'm far more concerned about the rise of Nazism and Monarchism in the USA. Even if we never have a Republican in any governing office again and the country continues to move further and further left, America has a lot of work to do to ensure these forms of tyrrany are never even considered as a viable alternative to Democracy.
The fact that these forms of governance survive in the hearts and minds of people is an indicator of a larger and more complex societal failing that spans the entire history of America. This is not some strange short term flash in the pan of Nazism and Authoritarianism, it is an insidious and vile tradition passed down from generation to generation, and we have only staunched it's slow cancerous growth by publicly shaming those who voice these views publicly. Obviously this has proven ineffective.
I think a more important question than whether one particularly sad excuse for a sad sack of shit may run for president again, is how do we make sure the Trump dynasty, and all dynasties, fade into obscurity until the last remnants of their legacy is a footnote that indicates we lived in a time period when humans, due to many generations of hoisting up those with the most lust for power into positions of power, nearly destroyed themselves. How do we make that happen?
Facism - and that is what Trumpism ultimately is - has always been fuelled by declining social security and rising social inequality. This provides the matrix for an ideology of us vs. them that is ultimately a distribution battle in a declining economy. Unless the USA (as well as many other nations esp. in Europe) solves this issue sufficiently well for the people at large, I see little hope for Trump or any of his clones to disappear from the political stage. That is also why the right is so eager to frame any initiative that aims to mitigate social precariousness as radical left/communism/socialism.