Marx believed that we could wipe out social inequities and Lenin tested those ideas on the Soviet Union. It was his dream to create a classless society. But reality set in, as it always does. And the results were devastating. Blood flowed through Russia’s streets. The Soviet elite usurped all privileges; sycophants were allowed some and the plebes none. The entire Eastern bloc, including Czechoslovakia, followed miserably.

I’m not sure Americans today appreciate quite how predatory socialism was. It was not — as Mr. Obama’s detractors suggest — merely a government so centralized and bloated that it hobbled private enterprise: it was a spoils system that killed off everything, all in the name of “social justice.”

What we need is not to strive for a perfect social justice — which never existed and never will — but for social harmony. Harmony in music is, by its nature, exhilarating and soothing. In an orchestra, the different players and instruments perform together, in support of an overall melody.

Today, our democracy, a miraculous gathering of diverse players, desperately needs such unity.