Lee McIntyre is a research fellow at Boston University and the author of “Post-Truth.” Jonathan Rauch is a senior fellow at the Brookings Institution and the author of “The Constitution of Knowledge: A Defense of Truth.”

In 2015, word spread online that a routine military exercise in the southwest, called Jade Helm 15, was a plot by President Barack Obama to impose martial law and seize everyone’s guns. The paranoia was “fueled by conservative bloggers and Internet postings,” the New York Times reported. So far did the claim spread that Gov. Greg Abbott ordered the Texas State Guard to monitor the exercise.

At the time, Americans responded to such bizarre online happenings with exasperation and bemusement. But the paranoia was fueled by more than conservative bloggers and Internet postings. Former CIA director Michael Hayden later said that Russian propagandists were behind the campaign. They were probing for vulnerabilities to disinformation — and found them. “At that point I think they made the decision, ‘We’re going to play in the electoral process,’” Hayden said.

Americans are no longer so naive about foreign attacks on our information space. The news media, the government and the public did a better job of recognizing and resisting information warfare from outside adversaries in 2020 than four years earlier.

But what if a far larger, more sophisticated and more ruthless disinformation campaign against American democracy originated within the United States? Would we recognize and respond to the threat? The answer so far is no — or, at best, only partially.

Most people regard Republicans’ #StopTheSteal campaign, also known as the “big lie,” as an attempt to re-litigate the 2020 election and pander to a radicalized, Trumpy base. It is that, but it is also a massive and devastatingly effective deployment of Russian-style information warfare against American democracy — by Americans themselves — with an eye toward the future. We should think of it not as a momentary partisan outburst but a kind of epistemic 9/11: a moment when a menace that has been developing for years reaches maturity and displays its full prowess.

Attacks on the concept of objective truth are not new. Left-wing attacks on objectivity date at least to the 1970s, with the rise of academic trends such as deconstructionism and postmodernism. Not long after, conservative media began attacking truth systematically, for example, through the rise of demagogues like Rush Limbaugh, who railed against the “four corners of deceit” (government, academia, science and the media).

The digital era raised the stakes by making misinformation easy to spread. GamerGate and online trolls refined viral outrage. Anti-vaccine groupspioneered digitally amplified misinformation. Russia spread divisive hoaxes and conspiracy theories. Misinformation became weaponized as disinformation — not a mistake but an intentional obfuscation created by those with interests at stake.

Specialists in the U.S. intelligence and military communities understand the power of information warfare to divide, disorient and demoralize the public. The Army Cyber Institute at the U.S. Military Academy has published a graphic novel warning against it. But few others have paid much attention, and many who do still blame cognitive bias and social media.

The rise of Donald Trump brought a turning point. He and his allies in conservative media and Republican politics seized upon Russian-style disinformation techniques and applied them to domestic politics. In his 2016 campaign, Trump lied so frequently and flagrantly that the media couldn’t keep up and the public lost track, a favorite Russian tactic known as the fire hose of falsehood.

With the #StopTheSteal campaign, the turning point became a point of no return. In April 2020, Trump launched a propaganda onslaught against mail-in balloting. Much as the Russians had used Jade Helm 15 to test their disinformation methods, Trump used the attack on mail-in balloting to organize the propaganda campaign he would launch if he lost the election. The already-high rate of Trump’s falsehoods ticked up sharply. After he lost, he and his allies unleashed a flood of exaggerations, lies and conspiracy theories through the White House, conservative media, social media and even the courts.

#StopTheSteal is not merely Trump’s way of being a sore loser or clinging to relevance (though it is those things). It is the most audacious disinformation campaign ever attempted against Americans by any actor, foreign or domestic. And it has been devastatingly effective. According to a recent Ipsos-Reuters poll, the majority of Republicans think the 2020 election was stolen, and almost half of independents either think the election was rigged or are unsure. Vladimir Putin could only dream of creating so much cynicism, doubt and distrust.

The “big lie” is a wake-up call, and not just about Trump. Even today, most scholars and commentators talk about America’s rising levels of polarization, extremism, and distrust of institutions and expertise as if they were natural disasters or products of generalized forces such as social media quirks, institutions’ failings and individuals’ gullibility. While those explanations have validity, they miss the more immediate threat: For years, Americans have been targeted with epistemic warfare — that is, with attacks on the credibility of the mainstream media, academia, government agencies, and other institutions and professionals we rely on to keep us collectively moored to facts. Those doing the targeting are nameable individuals and organizations, including Trump, conservative media outlets, Republican politicians, anti-vaccine groups and Russia’s Internet Research Agency.

Since epistemic warfare has proved its mettle so spectacularly in U.S. politics, it is likely here for good. Measures may allow us to fight back, such as revamping social media and teaching media literacy. But our primary means of defense is to be awake to the scope and origin of the threat. The first step toward winning the war on truth is to accept that we are in one.