Federalism is a political concept in which sovereign states are bound together by contract. The people themselves, through their sovereign state governments, delegated only a few enumerated powers (listed in Article 1, section 8) to this federal government by a contract, the Constitution. The contractual limitations where restated in the Bill of Rights, "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." It's pretty clear what this means. Any "law", passed by congress, that advances beyond the enumerated powers is VOID. To even greater lengths, the founders incorporated a separation of powers, splitting the federal government in to three branches in an attempt to create a series of checks against unwarranted legislation.
As soon as the constitution was ratified, attempts to invent new powers for the federal government began. In 1798 James Madison, commonly referred to as the father of the constitution, and Thomas Jefferson drafted the Kentucky and Virginia Resolutions, later becoming known as the "Principles of '98", which restated the limitations of the federal government and proposed a check of last resort for the states called Nullification. Jefferson asserted that "the government created by this compact [the Constitution] was not made the exclusive or final judge of the extent of the powers delegated to itself. Where powers are assumed which have not been delegated, a nullification of the act is the rightful remedy."
In his Report of 1800, Madison reminded Virginians and Americans at large that the judicial branch was not infallible, and that some remedy must be found for those cases in which all three branches of the federal government exceed their constitutional limits.
Alexander Hamilton, writing in Federalist No. 26, places hope in "the State legislatures, who will always be not only vigilant but suspicious and jealous guardians of the rights of the citizens against encroachments from the federal government, will constantly have their attention awake to the conduct of the national rulers, and will be ready enough, if any thing improper appears, to sound the alarm to the people, and not only to be the VOICE, but, if necessary, the ARM of their discontent."
If the federal government is allowed to hold a monopoly on determining the extent of its own powers, we have no right to be surprised when it keeps discovering new ones. If the federal government has the exclusive right to judge the extent of its own powers, it will continue to grow – regardless of elections, the separation of powers, and other much-touted limits on government power.
Today, Republican lawmakers in nearly a dozen states, including Idaho, Alabama, Kansas, Maine, Missouri, Montana, Oregon, Nebraska, Texans and Wyoming are re-introducing the idea of nullification to fight President Obama's health care overhaul.