The idea that we must not compare Trump to Hitler or our current turmoil to 1930s Germany is simply wrong. We must reject it—without losing respect for the horror of the Holocaust. If we do not learn from this history, the human failings that cause democracies to collapse will overtake our own.

There is a very small window of time in which to stop a growing autocracy before the window slams shut, according Timothy Snyder, a Yale historian who studies why democracies fail.

The idea that Americans are smarter, more politically astute, or in some other way superior to the Germans who were subjugated by Hitler doesn’t hold water, he says.

So what can one do in that small window of time? Snyder provides answers in his recent book On Tyranny: Twenty Lessons from the Twentieth Century. The first lesson is “Don’t obey in advance. Most of the power of authoritarianism is freely given.” The second lesson is “Defend institutions. It is institutions that help us to preserve decency.”

It is not enough simply to trust our institutions, he says. Institutions are not machines that automatically protect us, they rely on people. People make them work, and we must come to their defense.

“Ask not what our institutions can do for us,” he said yesterday in a television interview, “but what can we do for our institutions. When you say it can’t happen here you’re making it happen here.”

Consider President Trump’s attacks on two key institutions—federal law enforcement and the press—in the space of the few minutes Trump spent privately in the oval office with then-director of the FBI James Comey.

According to Comey—whose veracity, if not his judgment, remains unchallenged—Trump urged him to drop the FBI investigation of Michael Flynn. If that weren’t bad enough, he started the conversation by suggesting that Comey should jail reporters who publish leaked information.

We have no way of knowing whether Trump will turn out to be like Hitler or Stalin, but that does not mean we should ignore the warning signs. Snyder pointed out two examples:

First, before Trump fired Comey, he asked him twice over dinner for a promise of loyalty, which Comey declined. The demand for personal loyalty, Snyder said, is a hallmark of dictators, a demand for loyalty not to the constitution or to the country but to the leader. That kind of loyalty changes the character of the government.

Second, when Trump fired Comey, the head of the federal police force, he sent word of the firing by his personal security guard Keith Schiller instead of by normal government channels. Thus he suggested that his private security detail was superior to the FBI—just as Hitler’s SA and SS became superior to the German police.

These two examples don’t make Trump like Hitler, but they show how Trump’s mind works. And the history that we dare not ignore shows us what has happened when leaders have such instincts.

Snyder also drew attention to his lesson No. 10: “Believe in truth. To abandon facts is to abandon freedom.” Many Americans, both Republicans and Democrats, breathed a sigh of relief last night when they learned that Robert Mueller, a former FBI director, had been appointed special counsel to investigate Trump’s connection to Russia. Perhaps truth would regain its value and prevail.

Not much has been said about this, but President Trump has the Constitutional authority to fire the newly appointed special counsel. If he does that, our institutions will need all the support we can give them, because if the Republicans don’t rally for truth when that happens the small window will slam shut.