What is a power reserved specifically for the states?

The power to issue driver's licenses is a power reserved specifically for the states as it falls under the domain of state government authority. States have the constitutional right to regulate and administer their own licensing systems, which includes the criteria for obtaining a driver's license, the testing process, and the issuance of such licenses. This reflects the principle of federalism that allows states to manage their internal affairs and maintain the safety and welfare of their residents.

In contrast, declaring war is a power expressly reserved for the federal government under the Constitution. Regulating interstate commerce is also a federal responsibility, as it involves trade between states that transcends state lines. Establishing post offices is another function designated to the federal government, ensuring national communication and mail delivery systems are managed consistently across all states. This delineation of powers highlights the balance of authority between state and federal governments as outlined in the U.S. Constitution.