What does the "commerce clause" allow Congress to do?

The commerce clause, found in Article I, Section 8 of the U.S. Constitution, grants Congress the power to regulate commerce with foreign nations, among the several states, and with the Indian tribes. This clause serves as a critical foundation for federal regulatory power and has been interpreted broadly to encompass a wide range of economic activities that may affect interstate commerce.

The correct answer reflects this essential function by emphasizing both interstate and foreign commerce. This power allows Congress to regulate not just the buying and selling of goods and services between states, but also activities that have a substantial effect on such commerce, ensuring a unified economic system across state lines.

The other options do touch on important economic aspects but do not pertain directly to the core functions of the commerce clause. Taxing income from foreign investments, for instance, falls under Congress's power to levy taxes rather than its regulatory authority over commerce. Controlling trade policies with individual states can be influenced by the commerce clause, but it is more about the regulation of commerce rather than direct control of state policies. Establishing a national currency relates to Congress's power to coin money and regulate the value thereof, which, while vital to economic stability, is not the focus of the commerce clause itself.