There is, of course, one pesky little detail that always seems to get in the way of the efforts of states and localities to chart their own course and take the lead in policy innovation. It's the habit Washington has of setting obstacles in their path. Some of the biggest arguments right now are centering on the National Guard.

With the federal government deploying high percentages of Guard units overseas, governors have complained they're left short of help during fires, floods and other emergencies in their own states. Some of those complaints have been overblown. But now states have fresh reason to fear that Washington will take control of their Guardsmen, even while they're still at home.

The Posse Comitatus Act of 1878 forbids use of the military for domestic law enforcement, but it can be waived under an even older law, the Insurrection Act. That law allows the president to use the military at home under cases of severe civil disturbance or when basic rights are being violated. That's why presidents Eisenhower and Kennedy, for instance, were able to nationalize the Guard at critical moments during the civil rights era.

The original language of the Insurrection Act was vague, creating the presumption that it could not be invoked except in rare circumstances. Congress changed all that this year, inserting triggers to make it clear the law applies in cases of terrorist attack, natural disaster, epidemic or other public health emergency. Congressional sources say the change was made at the behest of the White House, which had floated the idea of putting generals, rather than governors, in charge of disaster response following Hurricane Katrina last year. "We see this as an expansion of the president's authority," says David Quam, of the National Governors Association, "a change to allow the possibility that the National Guard would be federalized."

It could have been worse. NGA produced a letter, signed by all 50 governors, protesting even stronger language that had been passed by the House. The final version, signed into law in October, says the president has to determine that domestic violence has escalated beyond the ability of state authorities to restore public order before he can intervene. But even with the modified language, that could be a mere formality. What's to stop a president, after all, from making such a determination? The likelihood is that in anything remotely resembling a future emergency, governors will be looking over their shoulders to see if and when Washington will swoop in on them.