2. What would be the effect on the United States if this decision had not

validated the idea that the Supreme Court has the power to judge

whether acts of Congress are unconstitutional?

This would have made the Congress as the ultimate power in the democratic system.

Explanation:

It is dangerous for the legislature or the executive to not have a system of checks and balances which is maintained by the judiciary in the system of democracy.

This would have been meaningless if the jury had no power to declare an act from the congress as unconstitutional. As it has this power, the legislature can be kept in check against compromising the constitution and getting away with it if it ever happens.