First what constitutes fascism? Fascism is a political ideology that seeks unity of the people against any perceived threat to that which forms the fundamental essence of a given society. This essence can be anything under the sun. For Mussolini it was "The Italian State", for Hitler it was "Das Volk", for Donald Trump it is what we could jokingly refer to as "'Merica." I joke but this is, among the reactionary Christian conservative base that form the bedrock of Trump's support, a legitimate and full conception of what the United States should be.
'Merica is best summarized as a white, Christian, Chauvinistic, Patriotic, Paternalistic, militaristic view of America that these people seem to think existed at some point in the past. I know not what point in American history fits this description but if you were to ask anyone who genuinely believes in 'Merica they will name some undefined past (likely the 1950s) where everything was perfect and is a time to which we should return. This is exemplified in Trump's slogan of "Make America great again" as if we weren't already the world's only superpower able to basically dictate world policy on most major issues but that is besides the point.
So, you may ask, how is this fascistic? The belief in 'Merica alone cannot constitute fascism. What makes Trump a fascist is his blatant statements to the effect of "if you are not with me then you are against me." But Trump also goes further by requiring his followers to subvert their own interests to those of 'Merica. Everything must be done to "make America great again" even if it means forcing Muslims to register for a "Muslim Database," calling for the rounding up and deportation of masses of Hispanic immigrants, or condoning the violent assault of a protester who had the courage to say "Black Lives Matter." Trump betrays his fascism not just on his calls for a return to 'Merica but of the need to cleanse the US in the pursuit of that goal.
Fundamentally fascism requires these three elements: a supreme uniting principle, mandating national unity in pursuit of that principle, and a willingness to cleanse or purge the nation of those who stand opposed to the principle or the unity required to achieve the principle. Trump and his followers seem to embody those principles. However Trump has one major problem, the Constitution. I do not believe that even if elected (which is a dubious proposition in itself) Trump would legally be able to do anything that he is calling for. Enter the fourth major characteristic of fascism: criminality. Most fascists rule through force of will or martial might. They do not usually attempt to legitimize their action through laws until long after the deeds are done, if they use laws at all. It is my firm belief that should Trump be challenged by the courts, or even Congress, he would unilaterally dismiss them and do whatever he wanted. This is the essence of criminality and I do not doubt for a minute that Trump would be willing to do whatever he feels is necessary to "make America great again."
This should scare everyone. If you don't believe Trump is capable of this, look at his treatment of the press. Even if he claims "liberal bias" we still have freedom of the press in this country, but you wouldn't think so looking at Trump's campaign. He routinely refuses to talk to media, corrals them during events to keep them from seeing what he doesn't want them to see, and (scariest of all) has an "enemies list" of media outlets he refuses to even allow to cover him. If you don't think this illustrates how Trump intends to lead then you are either burying your head in the sand or somehow think this is an acceptable means of governing in a democratic society.
I for one fear for the future of this country when a man like Trump stands a good chance of becoming the nominee for one of our major political parties. Should Trump be elected we, as socialist, communists, anarchist, and even sympathetic liberals, must be willing to join together in a Popular Front to defeat Trump by any means necessary, short of violence, to prevent the implementation of fascism in America that I fear is inevitable under a "President" Trump.