This post brought to you by "Duh!"
Bartels comes to this conclusion by examining what happened to income inequality from President Truman to President George W. Bush. He writes, "Under Democratic presidents, poor families did slightly better than richer families (at least in proportional terms), producing a modest net decrease in income inequality; under Republican presidents, rich families did vastly better than poorer families, producing a considerable net increase in income inequality."
He concludes that income gap increased under Presidents Eisenhower, Nixon, Ford, Reagan and both Bushes, while it declined under four of the five Democratic presidents who have served during this period -- all except Jimmy Carter. That pattern, he asserts, "seems hard to attribute to a mere coincidence in the timing of Democratic and Republican administrations."