Why the 10th Amendment was necessary:
“This government is to possess absolute and uncontroulable power, legislative, executive and judicial, with respect to every object to which it extends, for by the last clause of section 8th, article 1st, it is declared “that the Congress shall have power to make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution, in the government of the United States; or in any department or office thereof.”
A power to make all laws, which shall be necessary and proper; for carrying into execution, all powers vested by the constitution in the government of the United States, or any department or officer thereof, is a power very comprehensive and definite, and may, for ought I know, be exercised in such manner as entirely to abolish the state legislatures.”
“To their credit, the Federalist-dominated first Congress did add a reserved powers clause to the Constitution – the Tenth Amendment. However, this amendment contains a notable omission, which can be seen when it is compared with the similar Article II of the Articles of Confederation:
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Each state retains its sovereignty, freedom, and independence, and every power, jurisdiction, and right, which is not by this Confederation expressly delegated to the United States, in Congress assembled.
A proposal to insert the word “expressly” in the Tenth Amendment was defeated by both houses of Congress in 1789. Although the omission of this one word does not seem too significant, it would later prove to be another fatal flaw in the Constitution.”