Trump in FB
I think it's a mistake for Democrats to focus on calling Donald Trump a fascist.
Of course, Donald Trump probably is a fascist, or at least has fascist beliefs. He believes that a single man rules better than the messy back and forth of a democracy comprised of consensus-building mechanisms, institutions, and checks and balances. He believes the military should be loyal to him, not the Constitution. He believes his opponents should be imprisoned or expelled. He believes in "American blood," not American values.
But from the perspective of winning an election, Democrats would do better to call Donald Trump un-American.
I'll offer seven quick arguments, though I'm sure there are hundreds more out there.
First, and most importantly from the perspective of winning votes, my guess is that while "fascism" may sound bad to many voters, the concept does not viscerally alarm many people. It's not that voters like fascism; they're just not sure exactly what the word means. "Fascism" as a concept or historical movement last came up in middle school history class in the chapter on WWII. The last time the USA was actively at war with fascists, Donald Trump hadn't yet been born. (It doesn't help that the Soviet Union and Warsaw Pact, our sworn enemies from 1945–1990, constantly described the U.S. itself as fascist.)
Second, if the goal is connecting with undecided voters, it is far more powerful to call Trump un-American because he abhors so many beliefs that are foundational to the USA. Trump is anti-democracy. He actively works against core American principles of "liberty, equality, and justice for all." He wants to deploy troops against U.S. citizens. Even when his own VP's life was on the line and scores of police officers were being pummeled by thousands of his own supporters on January 6th, Trump watched gleefully and waited hours to lift a finger (assuming he types with just one finger) to try to quell an attack on the U.S. Capitol. Today, Trump calls those bashers of cops and trashers of history "heroes." Trump is anti–rule of law. He thinks Lincoln should have compromised on the South's demand to continue slavery. Trump admires authoritarian anti-democrats—who also happen to be our military and/or ideological enemies—like Xi Jinping, Vladimir Putin, Kim Jong Un, and Viktor Orbán.
Third, although (or maybe because) all of Trump's grandparents were born outside of the U.S., didn't grow up speaking English, and came here to avoid destitution or prison—Grandpa Drumpf was a German draft dodger, after all—Trump actively ignores the fact that most of today's U.S. citizens are descended from people who came here without visas, and that America's great strength as a society and economy is our diversity.
Fourth, Trump talks regularly about repressing freedom of speech and a free press — American values that are so bedrock that they're spelled out in the very First Amendment of the U.S. Constitution. The Founding Fathers—Washington, Hamilton, Jefferson, Franklin, Madison, and many others—had lived the First Amendment before they wrote it, conceiving and refining the idea of the United States in newspaper articles and speeches over the span of 50 years.
Fifth, Trump has said regularly that POWs and wounded American soldiers are suckers and losers. This alone makes Trump un-American. (And, BTW, mildly unfascist, since fascism glorifies warriors as the ultimate representatives of their country.)
Sixth, Trump has bragged on tape about molesting women ("grab 'em by the pussy") and gawking at naked teenagers at beauty pageants he hosted. While these aren't the acts of a fascist, per se, viewing women as objects to exploit rather than as agents of progress is certainly un-American.
Finally, Trump tries to wrap himself in the flag, claiming to embody America. Calling out Trump as unAmerican directly addresses the brazen fraud— just as in his bankrupt casinos, airline, steaks and university — in Trump's attempt to hijack the American flag and the institutions it signifies.