Fascism is a political ideology and system (sort of) that requires a whole lot of people to keep it in place. A "lone President" assassinating his political rivals in a single act is just a regular old dictator move. No fascism required.

Assassinating your political opponents using the military in the name of saving the nation fits quite neatly into the definition of fascism. You don't need the system to be fascist to be a fascist.

Since the prevailing view of Trump and MAGA Republicans is that they are fascist, it's not a stretch to point out that the proposal in the parent comment is far closer to "actual" fascism than the actions of an incompetent enabler.

Not endorsing the view, but that's how some people think. It would actually be incredibly interesting if he decided to commit political suicide by having Trump killed and spurring congress into amending the constitution to explicitly revoke the immunity. If presidents start murdering presidential candidates, we might be able to get together and pass a constitutional amendment. :)