As written in the U.S. Constitution
The power 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.
Bond v. United States- Decided June 16,2011
In a unanimous decision, the Supreme Court found that Bond had standing to argue that enforcing the Chemical Weapons Convention in this instance robbed areas of police power reserved to the states. Justice Roberts reasoned that actions exceeding the federal government's enumerated powers undefine the sovereign interests of the states.
In my own words
All power not used by federal government should be given to the states