Some years, they speak of “the final eradication in America of the age-old evil of poverty,” and then other years, the Democratic Party shifts its focus to “those who work hard, pay their bills, play by the rules . . .”

In 1972, the party promises “a guaranteed job for all,” offering to “make the government the employer of last resort.” But 20 years later, the Democrats pivot and nearly apologize for themselves, appealing to “Americans who may have thought the Democratic Party had forgotten its way” by saying that it now “rejects the big government theory that says we can . . . tax and spend our way to prosperity.”

If Republicans from 1960 to today moved in fairly linear fashion to ever-more conservative stances on the economy, taxes and a slew of social issues, the Democratic evolution over the same period was a more jagged series of experiments with activist and statist approaches, interspersed with more traditional paeans to family, faith and individual initiative....