Safeguards make it resilient.

Popular safeguards—the capacity of the public to enforce the distribu¬tion of authority—accords with the intuition of a wide array of federalism theorists that the ultimate force shaping federalism is the existence of a fed¬eral culture.16 The Framers repeatedly mention the ultimate backstop to the federal bargain would be "the people themselves". In wrapping up the Federalist, Hamilton mentions not the courts, but the people as those who would determine whether authorities had been overreached, for example in determining whether a tax was appropriate (Rakove 1996).17 Despite its theoretically-acknowledged importance, these popular safeguards of federal¬ism are elusive. There exist few attempts to measure them (but see Kam and Mikos 2007 and Cole and Kincaid 2006 and their subsequent surveys). The safeguard emphasized most memorably in the Federalist is structural: fragmentation of national powers and the incorporation of the states in to the federal government's decision-making (making it both federal and national).18 When the federal government's legislative power is separated by bicameralism and checked with an executive veto, policy approval must meet multiple majorities. When states appoint delegates to the federal legislature, federal encroachment is further inhibited. These formal elements of struc¬tural safeguards are most apparent, there are important informal channels as well. Riker (1964) promoted the potential of the party system to prevent cen¬tralization. The party system connecting political organizations and candi¬dates can be an important safeguard of the authority boundary. Political parties create interdependencies between local, state, and federal politicians, what Filippov, Ordeshook, and Shvetsova (2004) refer to as integrated parties. Federations with integrated party systems will see greater respect for the boundaries of federalism than those with disjointed party organizations because when a politician is dependent on his or her party, she is less likely to pursue policies that would damage the interests of politicians at other levels of government. In addition to the judicial, structural, political, and popular safeguards, states work informal channels, private and public, to press their interests as Congress writes laws, activity that was celebrated by Columbia law pro¬fessor Wechsler (1954) and has received much more attention from political scientists in recent federalism scholarship.19 The early input from the states reduces the extent that federal legislation oversteps its boundaries. Nugent (2009) decisively documents the way that states actively monitor, lobby, and often help to craft legislation. Ryan's study of environmental law (2011) supports Nugent's findings; she argues that federal-state bargaining is suf¬ficiently robust that the courts should limit their "safeguarding" activities. Dinan (2011) perceives a similar pattern with regard to the construction of the Affordable Care Act: states provided expertise, used their congressional delegations to threaten to block passage until they achieved desired com¬promises, and when needed, turned to the public to press federal officials to incorporate state demands. The co-decision-making blurs boundaries of responsibility, making it more difficult for voters to hold their representatives accountable (Bednar 2007). Depending on the channel used, states may work through structural safeguards (when they are incorporated into decision-making), political (when they work through their party organization), or popular, when they rally their own publics to contradict national action. And in some cases, their actions fall into a separate class of safeguards: intergovernmental retaliation, sometimes leading them to cooperate with one another in a collective de¬fense, as revealed by Woods and Bowman (2011), sometimes spurring them to push the boundaries of their own authority when they are displeased with the federal government's actions (Arizona's immigration policies, California's environmental standards, Massachussetts' health insurance policy). Indeed, one can find revivals of seemingly discredited arguments in behalf of state "nullification" of offensive national legislation or even threats to secede from an overbearing Union.