The Keating$-$Owen Child Labor Act prohibited the interstate shipment of goods produced by child labor. Reuben Dagenhart's father, Roland, had sued on behalf of his freedom to allow his fourteen$-$year$-$old son to work in a textile mill.

In Hammer v$.$ Dagenhart $(1918),$ Justice Day spoke for the Court majority and found two grounds to invalidate the law. Production was outside the power of Congress to regulate, and the regulation of production was reserved by the Tenth Amendment to the states. Day wrote that "the powers not expressly delegated to the national government are reserved" to the states and to the people.

Source: Oyez, Hammer v$.$ Dagenhart $(1918)$

$($A$)$ Identify the constitutional clause that is common to both Hammer v$.$ Dagenhart $(1918)$ and McCulloch v$.$ Maryland $(1819).$

$($B$)$ Based on the constitutional clause identified in part A$,$ explain why the facts of McCulloch v$.$ Maryland led to a different holding than the holding in Hammer v$.$ Dagenhart.

$($C$)$ Explain how the holding in Hammer v$.$ Dagenhart affected the balance of power between the states and the national government.