PRESIDENT TRUMP sent a message to Twitter — and by extension all communication platforms and outlets: If you cross me, you’ll be punished. Now, he has sent a message to the Federal Communications Commission: Cross me for misusing my powers in this way, and you’ll be punished, too.

Michael O’Rielly has served two terms on the FCC under two presidents, and was expected to serve another — until this week, when the White House announced it would withdraw his renomination. This unexpected notice came only days after Mr. O’Rielly gave a speech in which he exhorted listeners to “reject demands, in the name of the First Amendment, for private actors to curate or publish speech a certain way.” Such demands, not so incidentally, are precisely what’s contained in this spring’s executive order on social media sites, issued by the president after Twitter had the audacity to fact-check some of his more egregious tweets.

The order had instructed the Commerce Department, essentially, to petition the FCC to appoint itself arbiter of when a platform’s policies are not sufficiently “politically neutral.” Last week, the department did just that. The FCC has opened a public comment process, kicking off an evaluation of whether it has the congressional or constitutional authority to carry out the request. Both propositions are dubious at best; Section 230 of the Communications Decency Act was designed to allow platforms to moderate content as they pleased, not to prevent them from doing so. The Constitution was designed to enable free expression, not enable the government to stifle it. Mr. O’Rielly, though he has been careful to say the White House is within its rights to seek a review, appears to agree. Mr. Trump obviously does not.

Mr. O’Rielly’s confirmation had already been placed on hold by Sen. James M. Inhofe (R-Okla.) over a separate matter actually related to telecommunications policy: the FCC’s recent order to create a 5G network on a band of spectrum used for radar and GPS, which critics fear would endanger military operations. Any other president might at least have used this dust-up as a pretext if he was going to rid himself of a commissioner liable to vote against his preference.

But for Mr. Trump, the lack of a pretext is the point. The president wants Mr. O’Rielly, his fellow FCC commissioners and appointees across agencies to know what happens when they dare to put the rule of law first, just as the president wants Twitter, and Facebook, and all influential companies on the Internet or off to know how carefully they must tread with him in charge. This is a flagrant assault on the First Amendment under the guise of defending it, and an assault on those who seek to defend the right of free expression.

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