The way to prevent the growth of “Trumpism” – or of any statist ideology – is to cut off the very systemic power that makes it possible. In this case, it means fully investigating what happened on January 6 and holding anybody involved accountable for his or her actions – and unfortunately, both parties are pulling back from doing this out of their own particular political concerns.
Just as important is to limit the power of government, especially that of the executive branch, which in turn would limit the potential of a future president from becoming an authoritarian.
The approach to the investigation is discussed in "Trump's Back - So How Do We Prevent a Cover-Up of the Capitol Attack? [https://alcris2.medium.com/donald-trump-at-cpac-ba85a7374a2b?sk=54d475c7d03b186b87f2ad56b11d3516]. The article also links to how the events leading to January 6 were predicted in the spring of 2020 and what we can do to prevent their recurrence.