Final answer:
The "necessary and proper" clause and the Supremacy Clause in the U.S. Constitution have been pivotal in expanding the powers of the national government through Supreme Court interpretations, allowing Congress to enact laws in various policy areas and reinforcing the federal laws' precedence over state laws.
Step-by-step explanation:
The clause that helped the national government's authority grow significantly due to the Supreme Court's interpretation is known as the "necessary and proper" clause, also referred to as the elastic clause. This clause is located at the end of Section 8 of Article I of the U.S. Constitution.
It provided the basis for the doctrine of implied powers, which expanded the scope of congressional authority by allowing Congress to pass laws deemed necessary and proper for executing its enumerated powers. Furthermore, the Supremacy Clause in Article VI reinforced federal authority by establishing that federal laws, and the Constitution itself, take precedence over conflicting state laws.
These interpretations by the Supreme Court have had lasting impacts on the balance of power between the national and state governments and have allowed the federal government to play a significant role in areas not explicitly mentioned in the Constitution. Over time, this has included issues such as the regulation of interstate commerce, the provision of healthcare, and the enforcement of civil rights.