Under our Constitution, some powers belong to the federal government. What is one power of the federal government?

Why this is the answer

Naming any one of the four accepted powers answers this question: to print money, to declare war, to create an army, or to make treaties. The idea behind the list matters more than the list. The federal government is a limited government, meaning its powers are not whatever it decides to take but only those written into the Constitution. Everything else stays with the states. So the federal powers cluster around things only a single national government can sensibly do: one currency, one army, one voice in war and in agreements with other countries. Memory hook: money, war, army, treaties, the four jobs that cannot be done fifty times over.