Question

Which event of Jefferson's presidency changed the balance of power in American government?

A. The Corps of Discovery provided maps of western territories for the first time.
B. The Louisiana Purchase brought new land and people under the control of the United States.
C. The Embargo Act diminished trade in the United States and led to economic hardship for Americans.
D. The Marbury vs. Madison decision allowed the courts to strike down laws which were unconstitutional.

Answer 1

The answer is D: the Marbury vs. Madison decision.

Why: The event established the principles of judicial review to prevent any one branch from becoming too powerful.

Answer 2

D is what you want to go with.