I grew up with parents who liked the old line that they didn’t leave the Democratic Party—the Democratic Party left them. My father’s political heroes were Franklin Roosevelt and Harry Truman. My mother had been a campaign volunteer for Sen. Eugene McCarthy in 1968. But the party of George McGovern was not for them. As the left turned on “Amerika,” they kept faith in America.

Now it’s my turn to watch the Republican Party drift away. Whether the trend continues after the election remains to be seen, but already the GOP is...