Though Larry Bartels' forthcoming book, Unequal Democracy, will not be published until June, it has already provoked a lot of chatter online. At the end of March, Harvard economist Dani Rodrik posted a graph from the Bartels book on his blog. Rodrik called it "the most telling picture about the U.S. political economy I have ever seen."The graph shows the difference that the President's party affiliation makes to the distribution of income during the four years of the president's term. Rodrik interprets the graph as follows:

"When a Republican president is in power, people at the top of the income distribution experience much larger real income gains than those at the bottom... The situation is reversed when a Democrat is in power: those who benefit the most are the lower income groups. If you are in the bottom quintile, the difference between having a Democratic or a Republican president in office is an income gain (or loss) of more than 2 percent per year! Strikingly, compared to Republicans, Democratic presidents generate higher income gains for all income groups..."

Rodrik's post prompted a vigorous comment thread and Bartels, a professor of politics and public affairs at Princeton, was recruited as a guest blogger to answer his critics. (You can read his post here.)

Paul Krugman is sympathetic to Bartels, but skeptical. Mark Thoma, professor of economics at the University of Oregon, wonders why, if Congress writes the laws, the party tilt of Congress would not be more important than the party of the figure occupying the Oval Office. As for Tyler Cowen, he suggests an alternative interpretation of the graph: "Democratic Presidents live for the short run and we need a Republican President every now and then."