Democrats, when they’re feeling alarmed or mischievous, will often say that Ronald Reagan would not recognize the current Republican Party. I usually respond that John F. Kennedy would not recognize the current Democratic Party, and would never succeed in it.

Both men represented different political eras but it’s forgotten that they were contemporaries, of the same generation, Reagan born in 1911 and JFK in 1917. They grew up in the same America in different circumstances, one rich, one poor, but with a shared national culture....