Hitler was from a humble, working class background and spent most of his youth in poverty. Trump was born to privilege and power. Hitler was a brave soldier in the Great War, Trump was a draft dodger.

But both tried to gain absolute power through constitutional means, after first failing through a coup d'etat. Whether Trump is successful or not remains to be seen. But I don't think Trump will gain the support of the military either. Hitler didn't. The Army was only "following orders", and they waited until he was legally in power.

But like Hitler, Trump legally gained political office even without a majority of the popular vote,
and he took over by promising the people what they wanted, and by stimulating the economy so that the economic fears of the middle and working classes were suspended. And like Hitler, he did play on racial fears and hatreds already existing in the population. He exploited prejudice against foreigners, and blamed all the nation's problems on other countries, and domestic traitors. He perfected a propaganda press and mobilized militias of thugs to do his strong-arm work. Like Hitler, he took advantage of existing currents in society to do these things, those elements may have already been there, but he encouraged and promoted them. And of course, he lied. And his followers knew, they knew all the time, but just didn't care because he was "getting things done" and "sticking it to the Libs"..

After attaining power, both slowly but surely insinuated themselves into government by taking over public and civic institutions, and even purging the body politic of potential rivals. After a while, both managed to get into position to nibble away at all opposition to their rise, even among their own allies. It was done slowly, right from the start, and they didn't always get everything they wanted right away. But after a while people (especially their followers) finally felt taking the trouble to stop him just wasn't worth the effort. Apathy is just as effective as evil. I don't think Hitler wanted to exterminate the Jews at first, he just wanted to deport them. I don't think he wanted to conquer the world, he just wanted living space in the East. And I don't think he wanted a World War, but he wasn't afraid to start one.

As for Trump, I don't think he wants to be world dictator either, he just wants to help his businesses, and those of his friends and supporters, to prosper, and for his opponents to be powerless, humiliated and broken. He, and his kind, don't want to pay taxes and don't want their businesses regulated. Their idea of freedom is to be do anything they want. Hitler, on the other hand, never amassed a great personal fortune. He had snappy uniforms, rode around in a Mercedes and spent summers in a mountain retreat, but he wasn't in it for the money. Like all truly dangerous men, he actually believed he was doing the Right Thing.

Fascism has arisen several times in the 20th century; Italy, Spain, Portugal, Germany, several South American countries. It threatened several others, including the US, UK, France, but failed. It is not always the same, it varies according to historical and geographical circumstances, and the cultures and personalities of the nations and leaders involved.

But regardless of how it manifests in different cultures, Fascism is instantly recognizable. And it always winds up using violence to stay in power.
Wherever it has appeared, it has taken war or revolution to remove it. Only in Spain did Democracy return peacefully, but only after Franco died, 36 years after seizing power. And half a million of his countrymen died before he was finished.

And there is one other thing about fascism. When it is finally removed, what replaces it is often even worse.