The President's Patient Protection and Affordable Care Act (Obamacare) is unconstitutional on at least two levels. For one, the federal government cannot order a citizen to buy insurance, or pay a "penalty" like a criminal for not obeying the government's order to have heath insurance -- in fact, this very point is currently being litigated in the Supreme Court of the United States.
Obamacare is, in part, based on a belief that the "Commerce Clause" of the U.S. Constitution allows the federal government to control healthcare in general. The Commerce Clause has been used to prevent things from entering interstate commerce, but never to force a citizen to purchase goods or services. The Act goes further than the Commerce Clause has ever reached before and further than the U.S. Constitution allows.
On a different issue, the Act requires the States to expand their Medicaid programs without compensating them for doing so, a violation of the 10th Amendment. Even the Governor acknowledges that the State of Montana cannot afford Obamacare. The current Attorney General did not oppose Obamacare in federal court; Senator Shockley would have done so.