The Constitution in One Sentence: Understanding the Tenth Amendment

n a certain sense, the Tenth Amendment—the last of the 10 amendments that make up the Bill of Rights—is but a truism that adds nothing to the original Constitution. Since the federal government only possesses those powers which are delegated to it (Article I, Section 1), this amendment merely restates that all powers not delegated are in fact reserved to the States or to the sovereign people. In this sense, the Tenth Amendment concisely articulates the very idea and structure of a government of limited powers. The Tenth Amendment reinforces the federal system created by the Constitution and acts as a bulwark against federal intrusion on state authority and individual liberty. While the Supreme Court has countenanced a far-reaching expansion of federal power since the New Deal, Congress, as a co-equal branch of government, is not bound by these precedents and should uphold the concept of federalism embodied in this amendment.

http://www.heritage.org/Research/Reports/2011/01/The-Constitution-in-One-Sentence-Understanding-the-Tenth-Amendment