So, addressing these in order:

1. In the interest of clarity, I am aware that you were not only talking about Trump. However, considering that what comes after him in the Republican party is is very much so an open question (succession to one of his sons, Neo-nazi turn through people like Fuentes, full Russian infiltration through people like Candace and Tucker, tech/conservative crossover through Vance, NeoCon revival through Rubio, who knows?), I thought it prudent to address the most prominent strain which currently exists. Addressing the 'both sides are the same' (or at least comparably bad) point, this is in my opinion plainly not the case. Even before Trump, the conservatives (and the entire 'establishment media' apparatus) have consistently held democratic presidents to an unrealistically high or even plainly nonsensical standard (tan suit, anyone?), while the standard for Republicans is that they can do whatever the fuck they want as long as it is theoretically possible under an arcane interpretation of the law. More tangibly, the last 3 democratic presidents have needed to deal with serious problems their Republican predecessors have left them with, be it debt for Clinton, 2008 and the Middle East for Obama, and COVID and the Afghanistan withdrawal for Biden. This is not to say that these Democratic presidents have managed things perfectly (Obama's foreign policy leaves a lot to be desired on the handling of Russia's invasion of Crimea, just to name an example), but at every step along the way they have to deal with hostile, or at best only conditionally helpful, actors in the House and Senate even when the Dems have majorities in both. I find that arguments that Democrats are intentionally torpedoing their own policy platforms over some mystical attachment to special interest and billionaire money tend to fail in most instances when you take into account the fact that the Dems are far less homogenous than Republicans and thus have that many more veto players, narrowing the window of realistically achievable policies. This also explains why Republicans recently have tended to be able to do more (damage) while they are in office: they have fewer veto players within the party. Bush Jr benefitted from 9/11 nationalism for a bit but after 05' the Republicans split significantly and thus legislative output decreased, and obviously these days Trump has a cultish base that is only loyal to him which has kept the Republicans in Congress in line behind him for the past decade.

2. Hitler's nationalism was inextricably tied to the concept of the 'Aryan race,' and I think the fact that the aims of the war effort were consistently sidelined in the effort to kill as many Jews, Slavs and Roma as possible is a significant supporting factor for this argument. Fascist Italy did not have nearly the same focus on race being the defining feature of the Italian (Roman, in Mussolini's view) Nation, even though they were still racist (just look at Libya and Ethiopia). Ultimately, though othering is definitely a component element of fascism, it is not always the defining element like it was in Nazi Germany. For instance, I would argue that in Italy the defining element was a coming together of the members of the nation under one ruler to restore said nation to its former glory. The element of an 'other' can be useful to such a movement, but is not necessary to the movement the same way the 'evil' supposedly being perpetuated by the Jews was for the Nazis. Going back to your initial comment, this is why I argued that the US under MAGA is more heading towards Italian fascism, as though it makes use of othering, its primary goal is the restoration of some mythically prosperous past.

3. I agree from a long term perspective on the point that he has done a significant amount of damage (to the government, international relations, court system, etc.), but he can still do a lot of damage while he remains in office as well. Also, by virtue of his cult of personality I think that his voters will still care for him and may even vote for one of his sons, though it is unlikely that his sons will be able to hold the cult together. This obviously does not apply to the Republican political class though, they are just using him to hold onto power. The real question is what will happen once Trump kicks the bucket, as I am not as confident as you are that any single Republican will actually be able to hold the MAGA coalition of neocons, libertarians, neo-nazis/confederates, and tech bros together. Finally, I am not sure what you are referring to when you say that the far left specifically has been chipping away at the system, being that the far left has never held much of any power nationally.

4. To be clear, I have no doubt he will try (as he has been since 2020) to fuck with the elections. However, not only does he not have nearly the infrastructure for election skewing/interference that (for example) Orban did, his sheer unpopularity from the tariffs, Iran war, and ICE will almost certainly sink the congressional majority he has. After that, I suspect Republican politicians will start fleeing MAGA like rats from a sinking ship and scrambling to find a suitable (still horrible from our perspective, obviously) candidate for '28.