Socialism is more fashionable today than at any time since the Soviet Union collapsed. It’s back, and its major rival isn’t an ideology of unfettered free markets but right-wing populism. Theodore Roosevelt is a greater inspiration than Ronald Reagan to today’s young Republicans. The man most likely to be the next GOP presidential nominee, J.D. Vance, is more enthusiastic about Huey Long than Milton Friedman. Even the alternative “NeverVance” candidate insiders in Washington prefer – Secretary of State Marco Rubio – has made a point of saying capitalism must be “common-good capitalism.” Libertarians have disappeared, just as the national debt...