There is a striking similarity in both Hitler and Trump’s rise to power as highlighted by Leon Trotsky in his work Hitler’s Program (written in the time Hitler had come to power). To quote, 
“Hitler has been widely regarded as a demagogue, a hysterical person, and a comedian. Such opinions are the reflections of a diplomacy incapable of vision or understanding save in the most ordinary routine matters… Woe to those who do not awaken to this fact in time! The leaders of German labor refused to take Hitler seriously, they dismissed his program as an impossible blend of reaction and utopia. Today, as a result of their ghastly mistake, their organizations have been shattered to bits. What will happen if this mistake is repeated in the field of world politics?”

It is usually a sign of immaturity to compare a modern politician to Hitler, but when an actual fascist comes onto the national debate stage, no one takes these cries seriously. Potentially this is a horrendous mistake.

You can read Trotsky’s full essay here: https://www.marxists.org/archive/trotsky/1934/xx/hitler.htm