Bangladesh, Sept. 18 -- US President Donald Trump has escalated his campaign against left-wing extremism by officially designating the loose-knit Antifa movement as a “terrorist organization.” The announcement, delivered via his Truth Social account on the evening of September 18, follows the killing of conservative activist and podcaster Charlie Kirk, whose assassination has been linked by Republican leaders to political radicalization on the left.

The designation marks one of the most sweeping attempts to place a domestic activist network in the same legal and political category as foreign terrorist groups. While Trump and his allies argue that the move is long overdue, critics warn it risks inflaming political polarization...