Which governmental power is reserved for states according to the Constitution?

The power to conduct elections is indeed reserved for the states according to the Constitution. This authority is derived from the Tenth Amendment, which states that powers not delegated to the federal government nor prohibited to the states are reserved to the states or the people. This allows states to regulate the administration of elections, including processes such as setting the dates for elections, determining voter registration protocols, and overseeing the operation of polling places.

Other choices involve powers explicitly granted to the federal government. For example, the regulation of foreign commerce is a power that the Constitution reserves for Congress, allowing the federal government to oversee international trade matters. Establishing a postal service is also a power exclusively given to the federal government, ensuring nationwide communication. Lastly, the power to declare war is a responsibility that lies with Congress as outlined in the Constitution, ensuring a uniform strategy regarding national defense and military action. Therefore, conducting elections stands out as a power specifically allocated to the states, emphasizing the federal structure of governance in which states maintain significant authority in certain areas.