Significant contributions to the study of American politics and public policy, comparative political economy, and social theory. There is no doubt about his wide influence. He has shaped the study of the contemporary welfare state, arguing that the sorts of explanations that worked for the building of the welfare state do not work very well for its continuation in an age of retrenchment--and, anyway, there isn't much retrenchment. He has infused the idea of path dependence into political analysis, giving it theoretical depth and an empirical workout. Recently, in coauthored writings, he has advanced the idea of partisan asymmetry or imbalance in American politics.