DescriptionUnlike the assumptions contained in the federal plenary power doctrine, immigration policy in the United States is the result of conflict, collaboration and intense interaction between the states and the federal governments. Since the 19th century, immigration policy making has exhibited familiar patterns: when state and federal objectives have been aligned, states act as backers of federal policy, often using their legislative authority to strengthen federal immigration law. When preferences diverge, states become powerful lobbyists who can use their legislative authority to keep immigration-related issues on the top of the federal agenda. Large, electorally rich states are particularly effective pressure agents. Electoral and political concerns often lead the federal government to yield to state pressure and implement immigration reforms (often restrictive) that are consistent with state preferences.