Which of the following is a power reserved for the states?

Conducting elections is indeed a power reserved for the states, as established by the U.S. Constitution. The Constitution grants states the authority to decide the manner in which elections are conducted, including regulations for local, state, and federal elections. This power enables states to determine voting procedures, voter registration, and the overall electoral process within their jurisdiction, thus giving them significant control over their democratic practices.

In contrast, regulating foreign commerce, establishing a post office, and declaring war are powers that are specifically assigned to the federal government. The Constitution's Commerce Clause allows the federal government to regulate interstate and foreign commerce, while Article I, Section 8 grants Congress the power to establish post offices and declare war. These functions are necessary for maintaining national interests and ensuring consistency across states in matters that affect the entire nation. Therefore, the authority to conduct elections is a key example of a power uniquely reserved for state governance.