Even dictators have to give off the appearance of legitimacy. There were still courts and trials under Hitler and Stalin. They even had show trials.
Note that I'm not claiming that Trump is a dictator or has any intentions of becoming one, but I don't see how the use of the court system and/or trials would automatically mean that it's not a dictatorship.
As for the massacres, gulags, censoring opponents, etc., these are things to which the general public would not be privy, and it certainly wouldn't be reported in the press.