Citing half a century of jurisprudence, constitutional scholars envision an uphill battle for the challengers. Experts largely agree that the four Democratic-appointed justices are highly likely to uphold it, while only Justice Clarence Thomas has the sort of record that virtually ensures he will vote to strike it down. The other four Republican appointees -- Justices John Roberts, Samuel Alito, Antonin Scalia and Anthony Kennedy -- have a mixed record on federal power and are believed to be in play.
"For the challengers, it's like a best-of-seven series where you're down 3-0 and have to sweep the next four games to win," Orin Kerr, a George Washington University law professor, libertarian opponent of the individual mandate and former clerk to Kennedy, told TPM. "Those are not good odds."
The history of Commerce Clause jurisprudence took a major turn early last century. Prior to the New Deal era, the Supreme Court mostly used it to protect states from federal encroachments. Over time, industrial development led to an interdependent interstate economy, which created the need to regulate such activities on a national level. After the New Deal battles were settled, the Supreme Court's view of federal authority to regulate economic activities greatly broadened.
Since then, the high court has overwhelmingly supported congressional authority to make economic regulations -- from the 1942 Wickard v. Filburn case, which upheld laws restricting wheat production for personal consumption, to the 2005 Gonzales v. Raich ruling, which decreed (with the help of Scalia and Kennedy) that Congress may override state laws permitting medical marijuana patients to grow cannabis for personal use. The administration will argue that both laws reflected broad exercises of Congress's power on the scale of mandating insurance coverage.
"The concept here is about a body of laws developed over the last 60 or 70 years that has adopted a very expansive view of federal power," Kerr said. "The precedents don't foreclose the idea 100 percent, but they seem to point relatively directly to the conclusion that the justices will vote to uphold the mandate."
The two chief cases in modern history where the high court placed limits on the Commerce Clause were in 1995, to strike down gun laws, and in 2000, to overturn a piece of the Violence Against Women Act. But both those laws dealt with local and non-economic issues, and therefore had a more questionable premise under the Commerce Clause than the individual mandate.
In Raich, Scalia's concurring opinion declared that "where Congress has authority to enact a regulation of interstate commerce, it possesses every power needed to make that regulation effective." Liberals who hold out hope for winning Scalia's vote point to that opinion. It's an opinion that worries small-government libertarians because requiring the purchase of health insurance is a means of regulating interstate commerce, in part to prevent uninsured people from passing their medical costs on to taxpayers.
Roberts and Alito have not been on the high court long enough to rule on a broad Commerce Clause case. While Alito's view is seen as something of a mystery, Roberts has tipped his hand in favor of congressional power in other realms before.
In his confirmation hearing, under questioning about Wickard and Raich, the soon-to-be chief justice said he would have no intention of turning back the two precedents. The principles behind Wickard, he said, were "reaffirmed in the Raich case. And that is a precedent of the court, just like Wickard, that I would apply, like any other precedent. I have no agenda to overturn it. I have no agenda to revisit it. It's a precedent of the court."
And the Republican-appointed chief justice isn't afraid to cross ideological lines. In the 2010 U.S. v. Comstock case, Roberts joined the four liberal justices in a majority opinion decreeing that Congress has "broad authority" under the Constitution's Necessary and Proper Clause to indefinitely detain certain individuals beyond their prison sentencing (the plaintiff in the case was a sex offender). Like Kennedy, Alito concurred in the 7-2 ruling, but he wrote a narrower opinion, punting on the larger question.
Despite the favorable precedents, progressives have a nagging fear that the five Republican-appointed justices will hand down a partisan decision on the scale of Bush v. Gore, to deliver a blow to President Obama. After that unprecedented 2000 ruling, some liberals take little comfort in scholars' view that political pressure doesn't usually carry the day in the chamber, that the high court's longstanding tendency is to make gradual, not radical, shifts in jurisprudence on core Constitutional questions.
But the Obama administration likely only needs one Republican justice to win. And between Kennedy's track record of partisan independence, Scalia's jurisprudence in Raich and Roberts' occasional sympathy for federal power, they have cause for hope.
"I have thought this would not be and should not be a close question for the court, even if it takes a conservative approach," said Walter Dellinger, former U.S. solicitor general under President Clinton, at a panel organized by the liberal Center for American Progress. Overturning the mandate, he argued, "would be an extraordinary act of intervention by the Supreme Court."
Apart from that, Roberts may not love the mandate as policy, but he is keenly attuned to the institutional perils -- and the impact on his legacy -- of departing from "stare decisis" and reversing more than half a century of judicial precedent in one fell swoop.