On day two of the Supreme Court’s hearings on the Affordable Care Act, the justices were considering whether the law gives Congress the power to mandate that Americans purchase health insurance. As Sarah Kliff reports, some analysts said the oral arguments did not look promising for those defending the law:

What a difference two hours can make.

Going into Tuesday morning’s Supreme Court arguments, there was decently widespread agreement that the health reform law’s mandated purchase of insurance would survive the Court’s questioning. One poll released Monday, of 69 former Supreme Court clerks and attorneys who had argued there, found that 65 percent expected the provision to be upheld. On InTrade, odds hovered just about 67 percent.

But when the Court let out after two hours of oral arguments on the individual mandate, observers seemed a lot less certain. Jeffrey Toobin told CNN that he thought the arguments were a “trainwreck” for the administration, predicting now that the provision would get struck down. Donald Verrilli, who represented the Obama administration, stumbled over his words in his opening statement while Paul Clement, representing the law’s opponents, delivered a strong performance. On InTrade, the odds of the mandate being overturned shot up to 55 percent.

“I’ve been cautiously optimistic all along and today only pushed me a bit in that direction,” Virginia Attorney General Ken Cuccinelli told me when I caught him coming out of the Supreme Court. “I think the federal government failed to provide a constitutionality limiting principle.”

“Limiting principle” is a phrase that came up a lot in the Supreme Court Tuesday morning - 15 times, according to the transcript. It’s a legal concept you’ll probably hear a lot about in this afternoon’s analysis.

When courts review a new application of Congress’s constitutional authority, they historically wanted to see the government articulate a clear limit to those powers - they look for, in legal jargon, a “limiting principle.”

“If Justice Anthony M. Kennedy can locate a limiting principle in the federal government’s defense of the new individual health insurance mandate, or can think of one on his own, the mandate may well survive,” writes SCOTUSBlog’s Lyle Denniston. “ But if he does not, the mandate is gone.”

Is the health-care law good for small businesses? Olga Khazan reports:

Mike Roach, the owner of Paloma Clothing  in Portland, Ore., says health care reform has already helped his business’s bottom line — even though the law hasn’t been fully rolled out yet. The Affordable Care Act’s small business tax credit has shaved $5,500 off his company’s health-care premiums and allowed Roach to keep his workers on a good-quality plan even as costs rise.

Now, he looks forward to 2014, when a state-based exchange might allow him to negotiate even better rates.

“The new health care law has already started helping us,” Roach said. “Overturning it would send us back to the dark ages.”

But in Waco, Texas, the owner of an air-conditioning installation company, whose young employees tend to opt not to sign up for health plans,  said he fears that the cost of providing adequate coverage under the law will increase his overhead and drive up the end-cost of his products.

“We’ll adjust our business model for that, and that drives whether or not we hire,” said Capstone Mechanical owner Rick Tullis.

This week, the National Federation of Independent Business, along with 26 states,will argue that the health reform law’s provision mandating that everyone obtain health insurance — whether through an employer or a state-based pool — is unconstitutional, and thus the entire law must be overturned.

While the group’s legal argument is against the individual mandate, NFIB senior executive counsel Beth Milito said she also thinks its requirement that businesses with more than 50 employees offer health insurance is fundamentally flawed.

“Our members just want the government to stay out of their business,” she said.

But Tullis and Roach are actually both members of the NFIB. As their organization prepares to dispute the legal aspects of health care reform, their differing opinions illustrate the fact that there’s little consensus among small businesses as to the law’s merits, and business owners’ projections as to whether the law will be a net gain or loss depend almost entirely on their individual circumstances.

Bloomberg News recaps Monday’s proceedings at the Court and explains what lies ahead on Wednesday:

Yesterday’s opening arguments were on a question that could derail the case: whether the penalty for failing to get insurance amounts to a tax. An 1867 law blocks lawsuits over taxes that haven’t been imposed.

Justices including Stephen Breyer and Ruth Bader Ginsburg suggested they didn’t view an 1867 law as barring them from ruling this year. Ginsburg questioned whether health-care penalties would be taxes.

“This is not a revenue-raising measure,” Ginsburg said. “If it’s successful, nobody will pay the penalty and there will be no revenue to raise.”

The six hours of arguments spread over three days are the most the court has heard in a case in 44 years.

Tomorrow, the last day, the justices will consider what should happen to the rest of the law if they invalidate the insurance requirement. The court also will take up whether the law, by expanding the Medicaid program, unconstitutionally coerces states into spending more on health care for the poor.

More from The Washington Post:

Supreme Court considers main constitutional question in health-care law

Is Obamacare in trouble?

Can the White House win on health care?