What document outlines the structure of the United States government?

The Constitution is the foundational document that outlines the structure of the United States government. It establishes the framework for the national government, detailing the separation of powers among the three branches: the Legislative, Executive, and Judicial branches. Each branch has its own distinct functions, powers, and responsibilities, which helps to ensure a system of checks and balances. Additionally, the Constitution specifies the relationship between the federal government and the states, as well as the rights of the citizens.

Other documents play significant roles in American history but do not serve this primary purpose. The Articles of Confederation served as the first governing document but was ultimately found to be ineffective in creating a strong central government. The Declaration of Independence primarily outlines the reasons for the American colonies' separation from British rule, rather than detailing the structure of government. The Bill of Rights is essential as it enumerates specific individual rights and protections for citizens, but it does not outline the overall structure of government itself. Thus, the Constitution is the correct answer as it comprehensively lays out how the government is organized and operates.