The Progressive movement, the New Deal, and America’s involvement in two world wars encouraged sounding the alarm interposition by states, even if not identified as interposition. The explicit invocation of the term “interposition” surfaced in the 1950s by opponents of integration who sought a constitutional basis for white supremacy and racial inequality, particularly in opposition to Brown v. Board of Education of Topeka (1954) in which the Supreme Court rejected ‘separate but equal’ school segregation. After the Supreme Court repudiated interposition and nullification in Cooper v. Aaron (1958), use of interposition and nullification-like efforts resurfaced in resistance to federal laws and policies including: the Patriot Act of 2001, the Real ID Act of 2005, and the Affordable Care Act of 2010. A version of interposition termed “Judicial Federalism” emerged in the 1990s as a constraint on federal legislative power with the “anti-commandeering” principle in Printz v. United States (1997). Moreover, forms of “uncooperative federalism” and neo-nullification have marked recent efforts of states challenging federal policies and laws even as they fall short of nullification.