I very much doubt Trump could become a Hitler-like dictator. But I could certainly see a scenario where he shifts the Presidency in a significantly authoritarian direction, such that there is a real danger that he might be succeeded by someone who could become a genuine dictator,.
I would say the chances are at least even if Trump gets reelected and never gets checked down ballot (loses govs, or at least 1 house). He would be the first Republican ever to not get checked downballot.
In fact, I would say is if the Dems aren't rebuilt by 2023, Trump definitely does this and if a Republican succeeds him in 2025 if Trump does get checked, there is at least an even chance. Maybe even if Trump loses in both 2018 and 2020, 46 could be at risk.