What is the significance of federalism in the American political system?

Federalism, one of the key founding principles of the U.S. constitution, explains the balance and separation of power between central and local government. It was a political compromise between those of the original thirteen states who wanted independence and those who wanted strong central government, so as to, for example, form an army to protect against invasion. The theory of federalism is based on Locke's theory of limited government; Madison, a key Founding Father, argued that having the two levels of governmental power, federal and state, allowed 'double security' from tyrannical government. The constitution enshrines certain rights to states, such as the right to hold elections. We can see the independence of states on this issue through the differences in their presidential electoral systems; for example, Iowa holds caucuses and New York closed primaries. This example highlights one of the strengths of federalism; Iowa is a geographically large but sparsely populated state, meaning having polling booths for a ballot election for every citizen would be very expensive and impractical, and therefore a large meeting, a caucus, is preferable. We can see comparisons with the British state, which, despite being a largely unitary state, has elements of federalism in the case of elections; Scotland uses Additional Member System for elections to its devolved assembly, whereas elections to the federal government in Westminster use First Past the Post. Traditionally, the Supreme Court has held up this type of 'dual federalism', where the roles of federal and state government are separated. For example, 1995 U.S. v. Lopez ruled that Congress could not create gun-free zones and therefore frustrated federal government's efforts to impose gun control laws.However, over the course of the twentieth century, federal government has increased its power, often through constitutional specificities. The Supreme Court has played a role in this - one of the most significant rulings on federalism and power division was in 1958 Cooper v. Aaron, in which the Article 6 Supremacy Clause (placing federal and constitutional law as sovereign over state law) was confirmed. Furthermore, the increases in federal-level spending has increased the size of the state; for example, Bush expanded Medicaid by eighty million dollars, and Obama increased coverage by around twenty million people. The increased budget of federal government has given it power over states in the form of federal grants, which work out to around six hundred billion annually. A small population state like Arizona receives more from federal government than it does in state taxes, and cuts to its federal funding are seriously detrimental. On the other hand, a state as wealthy and large as, for example, California, is much more able to act independently of federal rules because the latter has little leeway over them. We saw this in California's willingness to frustrate Trump with its support for sanctuary cities. We can therefore see that federalism remains a fluid yet significant part of the American constitutional arrangement.