The impeachment drama now playing out in the House of Representatives has done much more than expose corruption in a presidential administration. It has exposed profound corruption in the way that we use language and the way that we claim to know things. These corruptions, I fear, will have far greater implications for our society than our president’s foolish attempts to extort opposition research from foreign leaders.

The problem begins, but does not end, with a once-obscure philosophical concept called “epistemic closure.”

As ten-dollar phrases go, “epistemic closure” earns its pay. It describes a phenomenon that can be difficult to get a fix on without a label. The term itself comes from academic philosophy and means something like “a philosophical system that cannot be successfully challenged because it does not accept anything as true that is not part of itself.”

As a term for political discourse, the term dates back to 2010, when conservative blogger Julian Sanchez used it to describe the growing tendency of conservatives to accept claims of fact only from conservative sources. It was intended as a criticism from inside the conservative movement. An epistemically closed system cannot tolerate any internal criticism, he explains, because “anything that breaks down the tacit equivalence between ‘critic of conservatives’ and ‘wicked liberal smear artist’ undermines the effectiveness of the entire information filter.”

What Sanchez described in 2010 has become an epidemic. By 2016, both political polarization and filtering technology had increased to the point that people of all political persuasions could spend much of their life consuming news, reading books, and interacting online with friends without ever encountering a fact that they disagreed with. This left us vulnerable to attack from an external enemy with the ability to manipulate both the presentation of facts and the mechanisms for verifying factualness.

Donald Trump did not invent epistemic closure, nor are his followers alone in relying on closed information systems. But practically everything that he has done since becoming president can be seen as part of an overall strategy to delegitimize any source of information with the potential to correct or criticize him. Newspapers, television, and radio? That’s “fake news.” Career diplomats and intelligence officers? Meet “the deep state.” Members of his own party who criticize him? These are the “Never-Trump Republicans,” also known as “human scum.” Indictment and conviction require only assertion; evidence is unnecessary.

And this should really scare us. Evidence is unnecessary because Trump has created an information environment that makes evidence irrelevant. “Facts,” he tells his supporters, can only be considered factual if he approves of their source. Every other way of knowing things must be dismissed and criticized, which creates a perfectly closed information system in which the only truth is Trump, and the only value is loyalty.

Donald Trump’s defense of his actions in Ukraine is unlike anything we have seen in this country, but very much like what people see regularly in authoritarian states. Nixon actually denied wrongdoing in the Watergate break in. And Clinton had enough respect for the truth to tell an actual lie, “I did not have sex with that women.” Both statements were ultimately proven incorrect, but, at least, they were the kinds of statements that could be proven incorrect. Yes they were false, but they were also falsifiable.

Donald Trump, on the other hand, has issued only weak and vague denials of any specific accusation or fact. He has chosen to defend himself with an aggressive attack on the idea that something called “evidence” can establish something called “truth.” For an evidence-based hearing to work, Americans have to agree that something beyond the control of Donald Trump can establish the truth of fact claims: science, history, testimony, expertise, Delphic oracles, Flying Spaghetti Monsters —anything will work, as long as the President can’t dismiss it with a tweet and a nickname.

Unless Americans and their legislators can be convinced that such a thing exists — that something other than Trump’s word can establish the truthfulness of truth — then Trump will win the impeachment battle and likely go on to a second term. And all it will cost us is our capacity to use language to mean things and our ability to declare things to be true.

Make no mistake about it, though, this is what a totalitarian society looks like. The whole point of totalitarianism is total control of every aspect of life. This includes the external things, like where one works and how one speaks. But it also means the internal things. Once we allow somebody to control our language and our way of knowing things, then we have given up what matters most; it is only a matter of time before they control everything else.