Portland, Ore., thinks of itself as a tolerant progressive city. Yet four weeks after a left-wing mob severely beat journalist Andy Ngo, there have been no arrests or charges for the assault.

Mr. Ngo was battered on June 29 as he reported on dueling protests. One demonstration included the far-right Proud Boys, and the counterprotest featured leftist groups associated with the extremist Antifa movement. Mr. Ngo has been a critic of Antifa’s militant tactics and its failure to disavow violence and vandalism, and that made him...