Last week on MSNBC's "All In with Chris Hayes," a guest mentioned the new unmentionable: Weimar. The guest was Bob Garfield, a liberal media critic, and he was discussing Donald Trump. Hayes was mildly disapproving of the reference. "I tend to stay away from Weimar comparisons for a variety of reasons," he said. That would make sense if only Trump himself did not constantly bring it to mind.

I must stop right here to emphasize what I will not be saying. I will not be calling Trump a fascist. I will not be saying he's an anti-Semite because, manifestly, he is not. I will not be smearing him with the clear bigotry of some of his supporters, although I fault him for not slapping down the haters with more energy. Still, the reference to Weimar is apt, not because Trump is another Hitler but because America might be another Germany.

Weimar is the charming German city that gave its name to the parliamentary democracy that was created following World War I and which Hitler crushed in 1933. It was never a robust democracy but it nevertheless was the government of Europe's most important -- and, in many ways, advanced -- country. Berlin in the early 1930s was a tolerant and liberal city. Many a Hollywood filmmaker got a start in Berlin. I cite Billy Wilder -- "Some Like It Hot," "Double Indemnity," "Sunset Boulevard" -- for one.

In a relative snap of the fingers, all that changed. Weimar's intellectuals, artists, actors, writers, architects (Bauhaus) and others fled. The precipitating event was, of course, Hitler's appointment as German chancellor. That was Jan. 30, 1933. Almost exactly one month later, the German parliament building, the Reichstag, was consumed by fire. A Dutch communist, Marinus van der Lubbe, was accused of setting it. (He was subsequently guillotined.) Hitler, declaring a vast communist threat, asked President Paul von Hindenburg for emergency powers. He got them. He kept them until he died.

Here is the relevance of Weimar. Donald Trump has shown a daunting disregard or ignorance of the Constitution and of law. Regarding the use of torture, he has said that the military must follow his orders -- even if they are illegal. More recently, he declared that flag burning should be a crime and that flag burners be punished by "perhaps a loss of citizenship or a year in jail." The remark was one of his off-the-cuff inanities -- ever since 1989, flag burning has been protected political speech, and citizenship, we'd like to think, is forever. The tweet -- so few words, so much meaning -- spoke to Trump's abysmal lack of knowledge but, more important, contained an emotional truth. Trump despises dissent and often reacts emotionally to setbacks or challenges.

Now, ask yourself what might happen if there was a huge terrorist incident on American soil. Might this man of little knowledge and no restraint attempt to suspend civil liberties? (After all, even Abraham Lincoln did.) His instinctive reaction to flag burning was all wrong. In addition, he holds the Nixonian view that the law is what he says it is. The courts have time and time again ruled otherwise.

Yet, I wonder if a compliant Congress and an even more compliant American people would balk at giving Trump any emergency power he seeks. His election was a stunner -- an eruption of anger and resentment that is putting an epochally unqualified man in the White House. So great was the urge to trash the status quo that Trump's lying, bragging, cheating, insulting and breathtaking ignorance did not disqualify him. Indeed, his very unsuitableness for the presidency immensely credentialed him. He is loved by many because he is loathed by others.

Already Trump has brought the Republican Party to heel with even his most vociferous critics -- Mitt Romney, for instance -- willing to discuss a Cabinet post. House Speaker Paul Ryan speaks of Trump as if he's just had a chat with Ben Franklin -- some good ideas, and let bygones be bygones -- but this passivity is actually good. Trump needs to be surrounded by political adults. Sooner or later, someone's going to have to throw a pitcher of cold water in his face. (Watch the hair!)

I have too much faith in America and its institutions to think that Weimar is the future. It is, however, a warning, not something that shouldn't be discussed, but something that should be mulled. The differences between Weimar Germany and contemporary America are significant but so, increasingly, are the similarities.

(c) 2016, Washington Post Writers Group