Since the mid–1990s, comparative research on welfare state evolution has contrasted the contours of postwar social policy expansion with the parameters of contemporary programme retrenchment. Paul Pierson's 1994 account of pension, housing and income support policies in the United Kingdom and the United States during the Thatcher and Reagan years proposed two core arguments with this literature: first, welfare state expansion and contraction were governed by fundamentally different dynamics; and second, even conservative, ideologically committed political executives found it hard to impose radical social policy changes. Because “the welfare state has proved to be far more resilient than other key components of national political economies.” Pierson has maintained, “retrenchment is a distinctive and difficult political enterprise.”