Don't get dragged down by doomers.
Will Trump and his ilk do all manner of dirty and fascist tactics to destabilize the country rather than let us have a fair democratic process? Absolutely.
Will it work? Absolutely unknown. The country is a much larger and more complicated place than other countries that have been subverted by dictators, Trump wouldn't need to do this once across one country, he has to do it across 50 individual states, each with it's own electoral systems and security methods. They are constantly overreaching and their only tactic, albeit and effective one, is to just make things confusing and chaotic.
This can only go so far. His "ICE army" isn't going to be strong enough to function as his own private police force because again, the country is too large. He would need hundreds of thousands of more agents just to barely scratch the surface. The marines are not going to be involved in any electoralism because they can't and no amount of bullying is going to make that change. Martial law is not a "magic switch" that just cancels elections, he's actually hoping enough people think it works that way I'm sure, but that will also get shot down by judges.
I'm not saying that the chances for massive corruption and losing the midterms is impossible, it's just that we have a lot of momentum and a lot of recent elections that have not been compromised, so if he had the power to do it, he would have by now.