Much has been written about how the Obamacare individual mandate is unconstitutional. Less discussed, however, is that another key part of the Senate’s version of Obamacare likely violates the Tenth Amendment. And some states are preparing to sue.

President Obama’s health care legislation is riddled with constitutional problems. The individual mandate, the employer mandate, even the buyoffs for Senators Nelson and Landrieu—they all raise constitutional issues, ranging from the limits on Congress’ power to regulate interstate commerce, to the taxing and spending authority of the government, to a little known—and from the commentary thus far, very little understood—General Welfare Clause.

South Carolina Attorney General Henry McMaster is leading a growing group of state attorneys general who are prepared to challenge parts of Obamacare. The Nebraska kickback that bought off Ben Nelson is the central focus of McMaster’s efforts.

But McMaster is also studying at an issue that almost everyone is overlooking. The Senate version of Obamacare includes a possible violation of the Tenth Amendment, which provides that any powers that either are not expressly granted to the federal government, or are not expressly denied to the states, are reserved to the people or to the states.

The Tenth Amendment is a constitutional provision that doesn’t mean what many people say it means. It’s casually tossed around by various conservative and libertarian talking heads as a catch-all objection to any federal program that the talking head doesn’t like.

It’s been interpreted much more narrowly than that by the judiciary. So much of the commentary suggesting that the individual mandate requires people to buy insurance is a violation of the Tenth Amendment is likely incorrect. As I’ve written previously, that mandate violates the Commerce Clause. While you can make a plausible argument that the mandate violates the Tenth Amendment, it probably won’t go anywhere in court.

But there’s another key provision in Obamacare that probably violates the Tenth Amendment: the state exchanges.

The Tenth Amendment went for so many years without being used to strike down any law that it came to be regarded as what is called a “dead letter” in the Constitution, meaning a provision that says some sort of obvious statement, but that isn’t actually used by the courts for anything.

Then, in the 1990s, the Supreme Court shocked the legal world by striking down two laws for violating the Tenth Amendment. The first was New York v. United States in 1992, where the Court struck down a federal law requiring states to pass state laws for the disposal of radioactive waste, and to issue regulations for implementing those laws. Then in Printz v. United States in 1997, the Court struck down a provision of the Brady Act—a federal gun-control law—that required state and local law enforcement to run background checks on handgun purchasers.

From these two cases emerged the anti-commandeering principle, holding that the Tenth Amendment forbids the federal government from commandeering—or ordering—any branch of state government to do anything. The states are sovereign and answer only to their voters, not to Washington, D.C.

Therein lies the problem for the Senate's Obamacare bill. It requires each state to pass laws setting up a statewide non-profit insurance exchanges. It then requires the states to pass regulations for implementing those laws. And it further requires the states to dedicate staff and spend state money to administer those programs.

In most respects, this is a straight-out repeat of those 1992 and 1997 cases. The main difference is that Obamacare violates the anti-commandeering principle in a far more severe and egregious way than those previous laws ever did.

This is really stunning. If New York and Printz had been decided as far back as 1910, then maybe you could imagine Congress deciding to roll the dice with a completely new Supreme Court a century later. But these are recent cases with conservative outcomes, and the only difference is that the Court has become a bit more conservative then it was in the 1990s when it decided those two cases.

How in the world do the Democrats plan on getting away with this?

Two possibilities. First, one aspect of this law that makes it worse than the laws struck down in the 1990s might save it in a constitutional challenge. The Senate bill says that if a state doesn’t create and run these exchanges, then the U.S. Department of Health and Human Services will directly come in and take over health insurance in that state.

This bullying is coercive, and incompatible with our federal system of independent states.

However, by making this threat that the feds will do it, it may shove this whole health care insurance system out of the Tenth Amendment and into the Commerce Clause, where Congress could control it.

It makes the law much worse in terms of the damage it could do. But it also gives rise to an argument that it is legal. Just because a law is stupid doesn’t mean it’s unconstitutional. In fact, Congress passes stupid laws all the time. And here it allows the Court to distinguish this case from New York and Printz.

The only other way they can hope to make this stick is to drag out any challenges to this law for a few years. Then, in Obama’s second term, he’d probably have the chance to replace one or two conservative justices with liberals, and then the Court could decide these cases differently.

But for that to happen, Barack Obama will need to get reelected in 2012. If Republicans can show the American people what’s at stake if Obama wins a second term, there’s a growing chance that the voters will deny him that opportunity.

Ken Klukowski is a fellow and senior legal analyst with the American Civil Rights Union.