How has federalism changed over time in the U.S.?

The correct answer highlights a significant evolution in the relationship between state and federal governments in the United States. Initially, the governance system operated under dual federalism, where state and federal governments had clearly defined and separate jurisdictions, often compared to a "layer cake." This model emphasized the independence of the two levels of government, with little overlap in their functions.

Over time, particularly throughout the 20th century, there was a shift toward cooperative federalism, characterized by a more intermingled relationship between state and federal authorities, akin to a "marble cake." This evolution was marked by increased collaboration on various issues, such as education, healthcare, and transportation, with federal funding often tied to state initiatives. Events like the New Deal and the Great Society further solidified this shift, as the federal government imposed more regulations and standards while providing financial incentives for states to partake in federal programs.

This transformation showcases how federalism in the U.S. has adapted to meet the needs of a changing society, reflecting a more cooperative and flexible relationship rather than a rigid or strictly dual structure. The other options do not accurately represent this nuanced evolution, as federalism has not eliminated state powers, merely centralized authority, or remained unchanging.