The amendment contains just one sentence: "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 is a bulwark of federalism, which allows states the freedom to adopt different policies reflecting their peculiar circumstances. It was meant as a check on those who would demand uniform practices from one end of America to the other.
Given the conservative preference for local control and distrust of national mandates, it's no surprise to hear Republicans asserting the central importance of this provision. In his book "Fed Up," Texas Gov. Rick Perry said attacks on the 10th Amendment have led to "unprecedented federal intrusion into numerous facets of our lives."
When he was governor of Minnesota, Tim Pawlenty said he might invoke the amendment to resist implementing President Barack Obama's health care reform. Former Massachusetts Gov. Mitt Romney used it to explain why his state health program is constitutional while Obama's is not. Rep. Michele Bachmann, R-Minn., is also fond of citing it.
They all seem to grasp the point of the 10th Amendment. As the Center for Tenth Amendment Studies at the Texas Public Policy Foundation says, it is to "protect our freedoms" and "prevent federal government power from controlling our everyday lives."
Liberals, by contrast, have never had any strong attachment to state sovereignty. Since the New Deal, they have regarded centralized power as the best way to advance the welfare state. They may favor state discretion when it favors their causes. But they don't pretend to be consistent on the issue.
Conservatives, however, do. Pretend, that is. When there is a conflict between state sovereignty and conservative policies, their reverence for the 10th Amendment abruptly goes by the wayside.
That became apparent several years ago, when the Bush administration asserted its power to prevent Californians from using medical marijuana after the state allowed it. It also tried to block an Oregon law allowing doctor-assisted suicide. Attorney General John Ashcroft had no qualms about mobilizing the fearsome resources of the federal government when states veered out of line.