Final answer:
The phrase that best completes the diagram on the effect of a Supreme Court ruling under John Marshall is 'Strengthened Federal Power', as his rulings supported broader federal authority and established key legal precedents.
Step-by-step explanation:
The Supreme Court rulings under Chief Justice John Marshall had a significant impact on the balance of power between the federal government and the states. The phrase that best completes the diagram on the effect of a Supreme Court ruling under John Marshall is A) Strengthened Federal Power. The landmark decisions made during Marshall's tenure, such as the McCulloch decision, established the doctrine of implied powers and the principle of national supremacy, thereby strengthening the federal government's role and limiting state intervention in federal policies. Key cases like Marbury v. Madison also established the precedent of judicial review, further affirming the power of the federal judiciary.