"I believe that nothing living can avoid the political today. The refusal is also politics; one thereby advances the politics of the evil cause."

Wrote Thomas Mann (to Hermann Hesse) in 1945, quoted in "Thomas Mann’s Brush with Darkness/How the German novelist’s tormented conservative manifesto led to his later modernist masterpieces" (The New Yorker). 

The author of the article, Alex Ross, continues:

If artists lose themselves in fantasies of independence, they become the tool of malefactors, who prefer to keep art apart from politics so that the work of oppression can continue undisturbed. So Mann wrote in an afterword to a 1937 book about the Spanish Civil War, adding that the poet who forswears politics is a “spiritually lost man.”... 

[During] the time that the novelist spent at [Princeton U]niversity between 1938 and 1941... Mann called for “social self-discipline under the ideal of freedom”—a political philosophy that doubles as a personal one. He also said, “Let me tell you the whole truth: if ever Fascism should come to America, it will come in the name of ‘freedom.’ ”

That's a great quote — "if ever Fascism should come to America, it will come in the name of 'freedom'" — and I googled it to see if today's anti-freedom leftists had used it against conservatives. 

Looking for Mann, I got Ronald Reagan: "If fascism ever comes to America, it will come in the name of liberalism." 

But it would be a mistake to think Reagan nicked it from Mann and that Mann was the originator of the "if fascism comes to America" clause. In the 1935 Sinclair Lewis book, “It Can’t Happen Here,” there's: “When fascism comes to America, it will be wrapped in a flag and carrying the cross.” 

You get the picture. There's a lot of If fascism ever comes to America, it will look like my opponents.

The "conservative manifesto" referred to in the New Yorker article title is "Reflections of a Nonpolitical Man." That book was recently reissued — here — and Ross is displeased by the new introduction, which he says "trivializes" Mann, putting him at "the level of an op-ed columnist":

The historian Mark Lilla, who wrote an introduction for the volume, thinks that Mann has something to tell us about ideological conformism in the arts today. It’s an obtuse reading of a work that Mann came to see as an artifact of his own political stupidity. In Trumpian America, the chief lesson to be drawn from the literary quagmire of “Reflections” is how educated people can accommodate themselves to irrationality and violence.

First published in 1918, the book is drenched in the patriotic fervor that overtook Mann’s intellect during the First World War. It seethes with contempt for Western democracy and with resentment of his brother Heinrich, who is never named but who appears in the guise of the Zivilisationsliterat (“civilization’s littérateur”). Heinrich decried the war in the name of cosmopolitan ideals, and in his contemporaneous novel “Der Untertan” he tracked the degeneration of German nationalism into chauvinism, militarism, and anti-Semitism. Artists should blaze a more enlightened path, Heinrich argued. Thomas responded in “Reflections” that war is healthy and enlightenment suspect. Art, he says, “has a fundamentally undependable, treacherous tendency; its delight in scandalous anti-reason, its inclination toward beauty-creating ‘barbarism,’ is ineradicable.”

Mann began backpedalling almost immediately, informing friends that the book would be better read as a novel. By 1922, he had reconciled with Heinrich and endorsed the Weimar Republic. As the years went by, he became increasingly embarrassed by “Reflections,” worrying that it had contributed to Germany’s slide into Nazism.

ADDED: Jonah Goldberg's book "Liberal Fascism" begins with a When-fascism-comes-to-America quote, and it's more recent than Reagan. It's George Carlin, speaking in 2005:

When fascism comes to America, it will not be in brown and black shirts. It will not be with jack-boots. It will be Nike sneakers and Smiley shirts. Smiley-smiley. Fascism—Germany lost the Second World War. Fascism won it. Believe me, my friend.