Relationships

Among states

Each state admitted to the Union by Congress since 1789 has entered it on an equal footing with the original States in all respects.^[18] With the growth of states' rights advocacy during the antebellum period, the Supreme Court asserted, in Lessee of Pollard v. Hagan (1845), that the Constitution mandated admission of new states on the basis of equality.^[19] With the consent of Congress, states may enter into interstate compacts, agreements between two or more states. Compacts are frequently used to manage a shared resource, such as transportation infrastructure or water rights.^[20]
Under Article Four of the United States Constitution, which outlines the relationship between the states, each state is required to give full faith and credit to the acts of each other's legislatures and courts, which is generally held to include the recognition of most contracts and criminal judgments, and before 1865, slavery status. Under the Extradition Clause, a state must extradite people located there who have fled charges of "treason, felony, or other crimes" in another state if the other state so demands. The principle of hot pursuit of a presumed felon and arrest by the law officers of one state in another state are often permitted by a state.^[21]
Regardless of the Full Faith and Credit Clause, some legal arrangements, such as professional licensure and marriages, may be state-specific, and until recently states have not been found by the courts to be required to honor such arrangements from other states.^[22] Such legal acts are nevertheless often recognized state-to-state according to the common practice of comity. States are prohibited from discriminating against citizens of other states with respect to their basic rights, under the Privileges and Immunities Clause.

With the federal government

Further information: Federalism in the United States

Every state is guaranteed^[23] a form of government that is grounded in republican principles, such as the consent of the governed.^[24] This guarantee has long been at the fore-front of the debate about the rights of citizens vis-à-vis the government. States are also guaranteed protection from invasion, and, upon the application of the state legislature (or executive, if the legislature cannot be convened), from domestic violence. This provision was discussed during the 1967 Detroit riot, but was not invoked.
As with state elections, elections for the federal government are generally administered by each state, and some voting rules and procedures may differ among states.^[25] In the federal Congress, each state is guaranteed two U.S. Senators, and at least one U.S. Representative from that state. The number of U.S. Representatives is limited to 435. These representatives are elected for two-year terms and are apportioned by relative population among the states every ten years. The U.S. Electoral College elects the president every four years and the states select the electors, which for each state's delegation are equal to its number of senators and representatives.
Since the early 20th century, the Supreme Court has interpreted the Commerce Clause of the Constitution of the United States to allow greatly expanded scope of federal power over time, at the expense of powers formerly considered purely states' matters. The Cambridge Economic History of the United States says, "On the whole, especially after the mid-1880s, the Court construed the Commerce Clause in favor of increased federal power."^[26] In Wickard v. Filburn 317 U.S. 111 (1942), the court expanded federal power to regulate the economy by holding that federal authority under the commerce clause extends to activities which may appear to be local in nature but in reality effect the entire national economy and are therefore of national concern.^[27]
For example, Congress can regulate railway traffic across state lines, but it may also regulate rail traffic solely within a state, based on the reality that intrastate traffic still affects interstate commerce. In recent years, the Court has tried to place limits on the Commerce Clause in such cases as United States v. Lopez and United States v. Morrison.^{[clarification needed]}
Another example of congressional power is its spending power – the ability of Congress to impose taxes and distribute the resulting revenue back to the states (subject to conditions set by Congress).^[28] An example of this is the system of federal aid for highways, which include the Interstate Highway System. The system is mandated and largely funded by the federal government, and also serves the interests of the states. By threatening to withhold federal highway funds, Congress has been able to pressure state legislatures to pass a variety of laws.^{[citation needed]} An example is the nationwide legal drinking age of 21, enacted by each state, brought about by the National Minimum Drinking Age Act. Although some objected that this infringes on states' rights, the Supreme Court upheld the practice as a permissible use of the Constitution's Spending Clause in South Dakota v. Dole 483 U.S. 203 (1987).