The answer to this one is 90% of the nation
In the USA, each branch of government has powers that have been defined as theirs by the Constitution. However, there is a notion of other powers that are not explicitly mentioned in it. In the case of Congress, such implied powers are deemed to be “necessary and proper”, that is to say, that it is understood that although they are not granted explicitly by the Constitution, they are logically and reasonably required to exercise those powers which are explicitly granted by the Constitution. Since the powers of coining money, acquiring territory and declaring war are explicitly granted by the Constitution to the federal government, the correct answer for this question would be building highway systems, which is an implied power (that also happens to be a concurrent power (a power that is exercised both by the federal and the state governments).
When the framers designed the US Constitution they did not give the Federal government much power so power was balanced between States and Central Government. But the Federal government has gained more and more power over time. At the same time, the States were restricted over the years, when the Framers did not imagine doing so.
Both of these situations can be good or bad. For example, making the States respect the Bill of Rights was a good thing when individuals had their basic rights stripped on a State level. So making only the Federal government respect the Bill of Rights did not make much sense.
At the same time, the Federal Government has shown much power that was not designed and showed a few issues over the years, especially with the Executive Branch that had in a few opportunities overstepped its powers.
One argument was that if the U.S. solely did a "test demonstration" of the atomic bomb, versus dropping it immediately on Japan, Japan would see the devastation of the bomb and would surrender on their own will without suffering huge losses.
