Walking through Midtown Manhattan, I stopped at a set of construction doors plastered with large posters from a campaign called Laboris.art — a Service Employees International Union project. It is paid for by SEIU’s Committee on Political Education, the union’s federal political action committee, and tied to its “Ball Without Billionaires” counter?programming for this year’s Met Gala. The slogans read “Billionaires Can’t Buy Power” and “Labor Is Power.” Standard left?populist messaging, until you notice the logo at the bottom of the poster: a crisp inverted red triangle.That symbol is antisemitic, and it carries two hate?filled histories — both histories of murder.The first is the Nazi concentration camp badge system. Beginning...