Executives at other platforms remain skeptical, and show no sign of jumping aboard. And the board will have to weather American domestic politics, with pressure from an anti-corporate left and a populist right embodied by Fox News’s Tucker Carlson (“an extraordinarily articulate polemicist,” Mr. Clegg said). And Mr. Clegg said he hoped the board would find a way to have its five American members directly involved in this ruling through “some bespoke arrangement so they can provide particular input and insight into this decision.” But there’s no clear mechanism for favoring Americans, and the connections between the board and real-world politics are already getting complicated. One prominent member, the Stanford law professor Pam Karlan, has recused herself to help with the Biden transition, an Oversight Board official said.

The board’s decision in the Trump case — due before the end of April — has obvious implications here in the United States, but it could also set the company’s policy in other big democracies with leaders of the same new right-wing populist ilk, like Brazil, India and the Philippines. For them, too, Facebook is a major source of power, and they’re now eying Palo Alto warily. The Trump ban is “a dangerous precedent,” an official in India’s ruling party tweeted. In Brazil, as in the United States, conservatives have begun shifting their followers to Telegram, a messaging service.