Lawsuits from 14 states challenging the constitutionality of the new national healthcare law face an uphill battle, largely due to a far-reaching Supreme Court ruling in 2005 that upheld federal restrictions on home-grown marijuana in California.
At issue in that case -- just like in the upcoming challenges to the healthcare overhaul -- was the reach of the federal government's power.
Conservative Justices Antonin Scalia and Anthony M. Kennedy joined a 6-3 ruling that said Congress could regulate marijuana that was neither bought nor sold on the market but rather grown at home legally for sick patients.
They said the Constitution gave Congress nearly unlimited power to regulate the marketplace as part of its authority "to regulate commerce."
Even "noneconomic local activity" can come under federal regulation if it is "a necessary part of a more general regulation of interstate commerce," Scalia wrote.
The decision throws up a significant hurdle for the lawsuit filed last week in federal court by 13 state attorneys -- all but one a Republican. The Virginia attorney general filed a similar, but separate suit.
The suits claim that the federal government has no right to force individuals to have health insurance -- a central provision of the new healthcare law.
"By imposing such a mandate, the act exceeds the powers of the United States under Article I of the Constitution," according to the suit from the 13 states.
But this week, Obama administration lawyers pointed to Scalia's opinion as supporting the constitutionality of broad federal regulation of health insurance, and most legal experts agreed.
In the healthcare legislation, signed by the president Tuesday, Congress required virtually all Americans to have health insurance beginning in 2014. Those who fail to do so could be assessed a tax penalty of up to $750 per year.
Legislators argued that the "individual mandate" was necessary because it would undercut the insurance market if individuals could just opt out of having health insurance. Freeloaders could wait until they were hurt in an accident or contracted a disease and then demand insurance coverage for their "preexisting condition."
The court's ruling in the 2005 case, Gonzales vs. Raich, "is an enormous problem" for those who contend that the healthcare mandate is unconstitutional, said Simon Lazarus, a lawyer for the Washington, D.C.-based National Senior Citizens Law Center.
"It clearly says Congress has vast regulatory authority over interstate commerce," he said.
David B. Rivkin, a Washington lawyer who is representing the 13 states, said the legal challenge rests on the principle that the federal government has limited powers.
"It is a matter of fundamental principle in the Constitution," he said. "Ours is a government of limited and enumerated powers. And there has to be a limit."
He also argued that the Constitution did not permit Congress to regulate health insurance, which has been traditionally under state control.
While the Bill of Rights put clear limits on the government's power to interfere with an individual's freedom of speech or free exercise of religion, the Constitution does not put clear limits on Congress' power.
Article I says, "Congress shall have the power to lay and collect taxes . . . [to] provide for the common defense and general welfare of the United States . . . [and] to regulate commerce."
Since the New Deal era of the 1930s, the Supreme Court has repeatedly said that the federal government can regulate almost anything that involves economic or commercial activity.
Several constitutional law experts said this week that it is somewhere between unlikely and hard-to-imagine that the Supreme Court would strike down the new healthcare law.
"In my view, there is a less than 1% chance that the courts will invalidate the individual mandate," said George Washington University law professor Orin Kerr, a former clerk to Justice Kennedy.
But some said the high court's conservatives could decide that the Obama administration and congressional Democrats had gone too far.
"When it comes to the hot-button, partisan issues that divide Americans, precedent rarely dictates how the court will rule," said Adam Winkler, who teaches constitutional law at UCLA.
The "court has already shown itself to be willing to break from long-standing precedent in major cases, and it won't likely be deterred by such case law in a challenge to healthcare reform," he said.
Critics of the new health insurance mandate often claim the Founding Fathers could never have envisioned the federal government telling individuals that they must take an action or buy a private product.
That, however, is not quite correct, experts said.
As one of its earliest actions, Congress passed the Militia Act of 1792, which was signed by President George Washington. It mandated that "each and every able-bodied white male citizen" must "be enrolled in the militia."
Hardly shy about imposing federal regulations on private citizens, the militia law said that each new recruit must show up within six months carrying "a good musket or firelock, a sufficient bayonet and belt, two spare flints, a knapsack [and] a pouch to contain not less than 24 cartridges suited to the bore of his musket or firelock."
Winkler also dismissed the argument that Congress cannot penalize someone for "doing nothing," such as not buying health insurance.
"If you don't believe me, just 'do nothing' this April 15 when your tax bill is due," he said.