Lee C. Bollinger is president of Columbia University and the author of several books on freedom of expression and the First Amendment. Donald E. Graham is a former publisher of The Post.

President Trump’s ongoing assault against Twitter may represent the most egregious violation of the First Amendment by a president since Richard M. Nixon went to war against this newspaper almost half a century ago.

Given the stakes, reaction has been strangely muted. Perhaps Americans have become accustomed to the president’s tweets and don’t believe he would do violence to his primary communications platform. Perhaps people are weary of the ceaseless controversies around social media.

Regardless, the seriousness of what’s happening and the threat it represents to one of our country’s most basic principles must be confronted.

Hard-won freedoms allow Americans to criticize the government and to voice any opinion without being punished for it. You cannot do so in countries such as China — but here, the First Amendment to the Constitution protects a level of uninhibited expression and wide-open debate found in few other nations. The First Amendment protects this newspaper, its readers and Twitter from punishment by the government. It does not, as the president seems to think, protect him from criticism.

To take this freedom for granted is to risk losing it.

Say what you will about Trump: He does not disguise his motives. On May 26, Twitter for the first time accompanied one of his tweets with a “fact-check.” The president had tweeted several times that former congressman Joe Scarborough, now an MSNBC host, should be investigated for the 2001 death of a young staffer in his office. Local prosecutors have said Scarborough had nothing to do with the woman’s death; there isn’t a shred of evidence that he did. The woman’s widower wrote a moving letter to Twitter chief executive Jack Dorsey begging him to remove Trump’s tweets.

Instead, Twitter attached a “potentially misleading” label to a May 26 Trump tweet casting aspersions on voting by mail. Trump immediately tweeted, “Twitter is completely stifling FREE SPEECH, and I, as President, will not allow it to happen!” The next day, his tweets grew more ominous:

“Republicans feel that Social Media Platforms totally silence conservatives voices. We will strongly regulate, or close them down, before we can ever allow this to happen.”

On May 28 came an executive order that proclaimed: “Twitter now selectively decides to place a warning label on certain tweets in a manner that clearly reflects political bias. As has been reported, Twitter seems never to have placed such a label on another politician’s tweet.”

The order had three parts: It instructed the Commerce Department to work with the Federal Communications Commission to review Section 230 of the Communications Decency Act, which shields social media companies against some lawsuits. It directed the Justice Department to draft a law that would have the same effect. And it ordered government agencies to reduce their advertising on platforms that engage in “viewpoint-based speech restrictions,” and designated the Justice Department to decide which platforms engage in prohibited speech.

This presidential order brought the federal government’s full power — the Justice Department, the Commerce Department, the FCC and the executive office of the president — to bear against Twitter. Unlike other public attacks by the president, which sometimes recede without subsequent action, there is no doubt about the threat being realized.

The Commerce Department has suggested an FCC proceeding. Last week, the Justice Department released the promised draft legislation. And the Office of Management and Budget has been enlisted to reevaluate government advertising on Twitter. The president was joined by nine Republican state attorneys general at a White House event last week who were later encouraged by Attorney General William P. Barr to use their authority to take action against social media platforms.

The specter of such intimidation inevitably leads to prior restraint and self-censorship. These assaults on Twitter are no less worthy of outrage than previous attacks on the traditional news outlets that dominated media years ago — about the time we ourselves first came to grips with the First Amendment’s importance to our way of life. Supporting the First Amendment often requires standing up for controversial people and causes.

The actions against Twitter are all of a piece, consistent with a posture of steady subversion of the press intrinsic to this administration and this president’s daily assaults on reporters and the news media.

Not since the McCarthy era has our country experienced such an effort to neuter the press and evade the government accountability that comes only through meaningful reporting. Consider what could lie ahead.

Twitter had every right to do what it did on May 26. Was Twitter’s action “right”? It doesn’t matter. The president cannot tell Twitter how his tweets must be handled any more than he can tell The Post what to write about his speeches. To use the power of the government to punish a company that won’t do what the president wants is a grotesque First Amendment violation.

No matter what you think of Twitter, social media companies or the applicable regulations, and no matter your political affiliation, everyone with a voice should speak out against the president’s actions. In particular, FCC Chairman Ajit Pai and his fellow commissioners should be watched closely. Will they simply do what the president asks?

Why are we so alarmed? To quote from the Trump executive order spawning this wave of government action against social media: “The freedom to express and debate ideas is the foundation for all of our rights as a free people.” That freedom isn’t threatened by Twitter. It is threatened by a powerful government using all the tools at its disposal to punish a company that didn’t act as the president wished.

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