The recent Supreme Court decision invalidating California's medical marijuana law has come under fire--correctly--from both the left and the right for undermining federalism. But observers have missed the real culprit in the court's flagging interest in balancing federal and state powers: the Bush administration.

Justices Clarence Thomas and Sandra Day O'Connor explained the problem in their dissents. Granting Congress the authority to regulate small amounts of marijuana grown in a backyard--marijuana that is never sold and never crosses state lines--makes a mockery of the efforts of the Constitution's framers to place limits on federal powers.

"If Congress can regulate this ... then it can regulate virtually anything," wrote Thomas, "and the federal government is no longer one of limited and enumerated powers."

But why blame the Bush administration too? In the medical marijuana case, it was the Bush Justice Department that decided to defend use of the federal drug laws to suppress homegrown marijuana.

That decision followed many others that show the administration's lack of interest in the proper balance of powers between state and federal governments.

Consider its position on these issues:

• The right to die: Then-Atty. Gen. John Ashcroft ordered that federal laws prohibit Oregon doctors from prescribing lethal doses of controlled drugs to terminally ill patients. He threatened to revoke the federal licenses of doctors who followed the Oregon law allowing physician-assisted suicide. Lower federal courts blocked him, but the administration has pursued the case to the Supreme Court, which will review it this fall.
• The president's support for Congress' efforts to block the death of Terri Schiavo: Congress issued an extraordinary directive to the federal courts to intervene in the normal workings of family law, an area that has remained under the control of the states since the birth of the republic. Fortunately, in that case, the federal courts proved more mindful of federalism than Congress and refused.
• Gay marriage: Last year, in response to "activist judges and local officials" in Massachusetts and San Francisco, the president proposed a constitutional amendment defining marriage as only between a man and a woman. The "Family Marriage Amendment" would override state laws experimenting with gay marriage.
• The No Child Left Behind Act: This 2002 Bush law reduces state autonomy in education by imposing uniform testing requirements. It uses the threat of significant restructuring of school operations if districts do not meet federal standards, all in an area that has historically fallen under the control of states.

The best of intentions may be behind these measures, but they follow a dangerous constitutional strategy. Demanding rigid, one-size-fits-all nationwide rules counteracts the benefits of federalism, which calls for decentralized governance. Federalism allows states to compete for residents and businesses. Some will choose to live in California because they are willing to trade high taxes for strong environmental rules, while others may want to live in Massachusetts because of gay marriage.

Worse, imposing national rules in these areas suppresses the ability of states to serve as "laboratories of democracy." As Supreme Court Justice Louis Brandeis observed, "It is one of the happy incidents of the federal system that a single courageous state may, if its citizens choose, serve as a laboratory; and try novel social and economic experiments without risk to the rest of the country."

Expand federal power and you retard the innovation that can answer difficult national problems.

Washington should only intervene when it's clear that a single federal rule will solve a nationwide problem that cannot be cured by individual states.

Federalism bestows a third benefit. The framers sought to create a competition between the states and Washington to prevent government from trampling on individual liberty.

Because of federalism and a separation of powers, James Madison wrote in the Federalist Papers, "a double security arises to the rights of the people. The different governments"--state and federal--"will control each other; at the same time that each will be controlled by itself."

Early in his presidency, Bush pledged to "make respect for federalism a priority in this administration," and he affirmed the founders' belief that "our freedom is best preserved when power is dispersed."

Now he should give the Supreme Court an example to follow by heeding his own words, remaining humble about the abilities of Washington to cure social problems and appointing federal judges who understand the importance of states.

John Yoo is a visiting scholar at AEI.