In the hands of a United States Supreme Court filled with justices who follow the Marshall ideology of federalism, the Tenth Amendment is a sop. It is a vacuous amendment with no substance. It is hollow. However, in the hands of a group of justices who reason similarly to Chief Justice Taney, such as the current Rehnquist majority, the Tenth Amendment is a powerful tool that can be used to empower the individual states and limit what powers the federal government can exercise over the states and their citizens. The Tenth Amendment is one of the most broadly defined and interpreted amendments. When invoked, the Tenth amendment has an interest in almost every aspect of our daily lives, including legalization of medical marijuana, abortion, gun free zones, driver's licenses, employment legislation, violence against women, and commerce. Whether the members of the U.S. Supreme Court follow the Marshall or Taney philosophy becomes very important due to the fact that the jurisdiction of the Tenth Amendment encompasses so many highly controversial topics. Therefore, the status of the Tenth Amendment is never a very stable position. The Tenth Amendment may be a powerless line on a piece of paper with one philosophy in domination, but with each newly appointed justice, the Tenth Amendment could easily gain enough power to be a strong friend to the states - and an unpleasant thorn to the federal government.
One way to define federalism is as a constitutional principle involving a distinctive territorial division of powers, usually an approach to representation within the national government, and mechanisms both legal and political to settle inter-level disputes. Another way would be to describe federalism as that which, as a matter of law, centers on the division of authority between the federal and the state governments, or as the dispersion of political power, or a system of authority constitutionally apportioned between central and regional governments.