Final answer:
The Supreme Court has limited the power of the national government over state governments, evident in key rulings like United States v. Lopez and decisions related to state enforcement of federal law and the Affordable Care Act.
Step-by-step explanation:
The statement that best describes the Supreme Court's trend in interpreting federalism since the mid-1990s is that the Court has limited the power of the national government over the state governments.
This trend is evident in several rulings that have curtailed federal authority, particularly under the commerce clause, to ensure that federal power does not encroach upon-state specific jurisdiction.
Notable cases include United States v. Lopez, which struck down the Gun-Free School Zones Act, and the 1997 decision that states and local law enforcement could not be compelled to conduct background checks for gun purchases mandated by a federal law, as well as the 2012 ruling regarding the optional expansion of Medicaid under the Affordable Care Act.