When Alexandria Ocasio-Cortez, a member of the Democratic Socialists of America (DSA), won New York’s 14th District primary in June, she immediately became a symbol of the potential future of the Democratic Party. Fittingly, she spent last month barnstorming the country for progressive candidates like her, exciting millennials, left-wing intellectuals and others about the possible resurgence of democratic socialism. Its adherents, out to distinguish themselves from the more moderate social democrats — previously the dominant tradition on the progressive left — offer online think pieces with headlines like “Social Democracy Is Good. But Not Good Enough” (from Jacobin ), “Democratic Socialism Isn’t Social Democracy” (also Jacobin ) and “It’s not just New Deal liberalism” (from Vox).

Indeed, these are distinct traditions with different goals and priorities, strengths and weaknesses. And if the Democratic Party’s left flank shifts from one to the other, it should know about the drawbacks that democratic socialists have historically posed for democracies. In the end, voters and lawmakers need real-world solutions for governing problems, and democratic socialists — with their frequent determination to let the great be the enemy of the good — have a poor record of providing them.