Governmental public health in the United States: the implications of federalism.

Governmental public health activities in the United States have evolved over time as a result of two forces: the nature and perceived importance of threats to the population's health and safety, and changing relationships among the various levels of government. Shifts toward a more state-centered form of federalism in the second half of the twentieth century weakened key aspects of the governmental public health enterprise, including its leadership and coordination, by the century's end. These developments challenge governmental public health responses to the new threats and increased societal expectations of the early twenty-first century.