10th Amendment.
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. ”
[edit] History and case law
The Tenth Amendment is similar to an earlier provision of the Articles of Confederation: "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."[1] After the Constitution was ratified, some wanted to add a similar amendment limiting the federal government to powers "expressly" delegated, which would have denied implied powers.[2] However, the word "expressly" ultimately did not appear in the Tenth Amendment as ratified, and therefore the Tenth Amendment did not amend the Necessary and Proper Clause.
The Tenth Amendment, which makes explicit the idea that the federal government is limited only to the powers granted in the Constitution, is generally recognized to be a truism.
“If the federal government has the exclusive right to judge the extent of its own powers, warned the Kentucky and Virginia resolutions’ authors (James Madison and Thomas Jefferson, respectively), it will continue to grow – regardless of elections, the separation of powers, and other much-touted limits on government power.”
–Thomas E. Woods
Slippery slope indeed, considering how this Admin, just loves and adheres to the Constitution.