President Obama and the Democrats have decided “income inequality” is the major domestic issue confronting Americans. But a new study by liberal economists challenges many of the president’s and his political allies’ assumptions about the growing gap between rich and poor.

“Where Is the Land of Opportunity? The Geography of Intergenerational Mobility in the United States,” published this week by the National Bureau of Economic Research, debunks shibboleths of both the left and the right. Conservatives often assert that economic mobility is greater in the U.S. than it is almost anywhere in the world, but the data don’t support it. There is greater mobility in many other nations than there is in the U.S. — the Scandinavian countries, Canada and Australia, for example. But liberals are wrong about whether it is more difficult now than in the past for Americans to move up the income ladder, according to the study. Moreover, there is substantial variation in economic mobility based on a variety of geographic factors.