Which of the following cases is a classic example of dual federalism?

Dual federalism is characterized by a clear separation of powers and responsibilities between the national and state governments, often described as a "layered cake" approach to federalism. Each level of government operates independently within its own sphere of authority. In the case of Plessy v. Ferguson, the Supreme Court upheld state segregation laws under the "separate but equal" doctrine, which reflected the prevailing attitudes of the time regarding state sovereignty over social issues. This case exemplifies dual federalism because it reinforced the idea that states had the power to enact and enforce laws related to race and social order, operating independently of national standards.

The other cases mentioned involve significant federal intervention or expansion of civil rights, which are more indicative of cooperative federalism, where layers of government work together to address complex social issues rather than maintaining separate jurisdictions.