At Reason, The Republican Party is a fickle friend to the 10th Amendment. A quote:
Liberals...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.
He has new company among the GOP presidential aspirants, who support the 10th Amendment except when they don't. When New York legalized same-sex marriage, Perry first said, "That's New York, and that's their business, and that's fine with me." But he soon reversed course, endorsing the Federal Marriage Amendment, which says marriage "shall consist only of the union of a man and a woman."
We support states' rights and state sovereignty. Country too big, too varied, too diverse, for a one-size fits-all.