ESSAY ALAN S. BLINDER

Many Americans know that there are economic policy differences between Democrats and Republicans . But few are aware of two important facts about the post-World War II era, both of which are brilliantly delineated in a new book, “Unequal Democracy,” by Larry M. Bartels, a professor of political science at Princeton University in New Jersey. Understanding them might help voters see what could be at stake, economically speaking, in November.
I call the first fact the Great Partisan Growth Divide. Simply put, the United States economy has grown faster, on average, under Democratic presidents than under Republicans.
The stark contrast between the booming Clinton years and the dreary Bush years is familiar because it is so recent. But while it is extreme, it is not atypical. Data for the whole period from 1948 to 2007, during which Republicans occupied the White House for 34 years and Democrats for 26, show average annual growth of real gross national product of 1.64 percent per capita under Republican presidents versus 2.78 percent under Democrats.
Such a large historical gap in economic performance between the two parties is rather surprising, because presidents have limited leverage over the nation’s economy. Most economists will tell you that Federal Reserve policy and oil prices, to name just two influences, are far more powerful than fiscal policy. But statistical regularities, like facts, are stubborn things. You bet against them at your peril.
The second big historical fact, which might be called the Great Partisan Inequality Divide, is the focus of Professor Bartels’s work.
It is well known that income inequality in the United States has been on the rise for about 30 years now . But Professor Bartels unearths a stunning statistical regularity: Over the entire 60-year period, income inequality trended substantially upward under Republican presidents but slightly downward under Democrats, thus accounting for the widening income gaps over all. And the bad news for America’s poor is that Republicans have won five of the seven elections since 1980.
The Great Partisan Inequality Divide is not limited to the poor.
To get a more detailed look, Professor Bartels studied the postwar history of income gains at five different places in the income distribution.
When Democrats were in the White House, lower-income families experienced slightly faster income growth than higher-income families - which means that incomes were equalizing. In stark contrast, there was much faster income growth for the affluent when Republicans were in the White House - thus widening the gap in income.
The sources of such large differences make for a slightly complicated story. In the early part of the period - say, the pre-Reagan years - the Great Partisan Growth Divide accounted for most of the Great Partisan Inequality divide, because the poor do relatively better in a high-growth economy.
Beginning with the Reagan presidency, however, growth differences are smaller and tax and transfer policies have played a larger role.
We know, for example, that Republicans have typically favored large tax cuts for upper-income groups while Democrats have opposed them. In addition, Democrats have been more willing to raise the minimum wage, and Republicans have been more hostile toward unions.
The two Great Partisan Divides combine to suggest that, if history is a guide, an Obama victory in November would lead to faster economic growth with less inequality, while a McCain victory would lead to slower economic growth with more inequality.