How quickly, in a crisis, the unthinkable can become reality. If it might have seemed fanciful a week ago that a US president could incite insurrection or face a second impeachment in a single term, so, too, would the prospect of social media platforms barring the “leader of the free world”. The bans by Twitter, Facebook and Instagram on President Donald Trump raise profound issues — of freedom of speech, and the precedents they may set for less free societies. While the “permanent” nature of Twitter’s suspension is questionable, however, not acting would have created even bigger risks.

In the exceptional circumstances of America today, platform companies were right to suspend Mr Trump’s access at least until the end of his presidential term. The president has glorified violence and egged on a challenge to US institutions that left five dead. Critics are right to say the move came cynically late. The president has repeatedly flouted the platforms’ user rules. Had the platforms acted earlier to remove offending presidential posts selectively, the need for tougher actions might have been averted.

Police had good reason for concern, moreover, that the president’s supporters were using both mainstream and more niche platforms to plot further violence. That justifies moves by Apple, Google and Amazon to restrict access to Parler, the “alt-tech” Twitter alternative beloved of the radical right.