The Second Circuit’s recent unanimous decision in Knight First Amendment Institute v. Trump finding that the president cannot block critics from his Twitter account’s feed was anything but surprising for those who even have a passing knowledge of the First Amendment.

The president brought the ruling on himself when he blocked a handful of critics—out of thousands—from replying to his tweets and supporting other critics. After all, it was the president who, despite enormous criticism during and after the 2016 campaign, insisted that he would continue to use the platform to communicate directly with the American people. Rather than bow to those who claimed his aggressive use of the platform was unpresidential Mr. Trump declared it to be modern presidential communication that he would not abandon. Other elected officials on both sides of the aisle have followed suit.

So it was not unexpected that the court found that the account and its webpage bear all the trappings of an official, state-run account and that since taking office he has consistently used the account “as an important tool of governance and executive outreach.” “Because the President, as we have seen, acts in an official capacity when he tweets, we conclude that he acts in the same capacity when he blocks those who disagree with him,” the court said.

A little context here for those who have not been part of this Twitter spectacle. Maybe these critics had a particularly sharp blade in their language or maybe the president or his staff were particularly sensitive to it, but if you’ve ever taken a look at the president’s Twitter feed, it is a primer for both inventive and sarcastic trolling and worshipful extolling of his agenda. Users comment not only on Mr. Trump’s tweets but on many of the more popular comments; these chains of tweets often stretch into the hundreds.

There can be little doubt these exchanges are at the heart of the open, robust debate about issues that New York Times v. Sullivan envisioned when it added a constitutional dimension to the public’s right to criticize public officials in the conduct of their duties. The court concluded just that by noting the irony of a case about whether someone can stifle such speech: “This debate encompasses an extraordinary broad range of ideas and viewpoints and generated a level of passion and intensity the likes of which have rarely been seen,” the court wrote. “This debate, as uncomfortable and as unpleasant as it frequently may be, is nonetheless a good thing.”

And so the Second Circuit’s analysis was relatively simple: viewpoint discrimination in a public forum violates the First Amendment and social media is entitled to the same First Amendment protections as other media. Replying to a tweet, retweeting and liking a tweet are all expressive conduct that such blocking inhibits.

While the government—ironically speaking for Mr. Trump—agreed that the plaintiff’s criticism was protected speech, they argued that blocking speech on Twitter did not burden that speech. The court rejected that because those who are blocked can no longer participate in the interactive features related to the account.

“While he is not required to listen, once he opens the interactive features of his account to the public at large, he is not entitled to censor selected users because they express views with which he disagrees,” the court ruled, rejecting arguments that there was a technical workaround the blocked users could use and pointing out that the government conceded these workarounds themselves burdened speech. And while the court agreed Mr. Trump’s pronouncements were government speech, which does not have to maintain viewpoint neutrality, the interactive features such as retweets, replies and likes, are not government speech.

This ruling is already having a trickle-down effect. Two critics of freshman Rep. Alexandria Ocasio-Cortez (D-NY) have sued, claiming that her website, like the president’s, is a public forum and they have been blocked. And Twitter feeds and Facebook pages throughout the country run by state and local governments with an eye toward extolling the party line while shutting down criticism should beware. While some courts have come down on these issues in the past, this is the strongest statement yet in favor of speech and debate about public issues—and a public official—that will hopefully have the First Amendment’s back for years to come.