How could members of the Supreme Court possibly seriously consider the argument that ObamaCare's individual mandate to purchase health insurance is unprecedented and unconstitutional? The quality of the arguments? The presence of a genuine legal debate? No, if you ask the law's liberal cheerleaders, there can only be one answer: pure partisan politics.

Since challenges to ObamaCare first took off, liberals have been laying the groundwork for a stepped-up public campaign against the Supreme Court should any part of the law be struck down. If the Court decides against the health care overhaul, it's clear that President Barack Obama and his defenders will make the Court a significant issue in the 2012 presidential campaign. Are liberals right to pin this week's developments on rank partisanship? In one sense there are. But the partisanship that's at fault here is their own.

From the beginning, ObamaCare's backers presumed that the nation's legal institutions would be on their side—and wouldn't require much effort to convince. Going into this week's Supreme Court arguments over the fate of the 2010 health care overhaul, liberal analysts were supremely confident. Since the law's passage, they'd been predicting that the law would pass constitutional muster with ease. In February 2011, Harvard Law Professor Laurence Tribe reassured readers of The New York Times that even conservative justices would not buy the challengers' arguments, insisting upon the "clear case for the law's constitutionality." Andrew Koppelman, writing in The Yale Law Journal Online, declared the mandate's constitutionality "obvious."

Liberal analysts maintained their enthusiasm even after multiple losses in the lower courts. The case against the mandate is "analytically so weak that it dissolves on close inspection. There's just no there there," wrote former New York Times legal correspondent Linda Greenhouse a few days before the arguments began. Slate's Dahlia Lithwick seconded Greenhouse and argued that the health law's individual mandate to purchase health insurance "is a completely valid exercise of Congress' Commerce Clause Power." Mother Jones' Kevin Drum suggested that the pro-ObamaCare side had a "slam dunk legal case."

But after three days of Supreme Court back and forth in which many of the justices seemed willing to entertain and perhaps even accept the basic premise of the argument against the mandate—and possibly the rest of the law as well—liberals seemed much less confident.

After this week's arguments concluded, Jeffrey Toobin, a legal analyst for CNN and The New Yorker who had predicted that the law would easily secure Supreme Court approval, declared that "the last three days were a disaster for the Obama administration." Some were downright distraught: Lithwick warned that Supreme Court's skepticism that Congress might not be able to compel individuals to purchase a private product constituted a "dark vision of freedom." An even bigger surprise was that Solicitor General Donal Verrilli, who argued the case in front of the Supreme Court, seemed unprepared for the tough questioning from the justices.

What can explain liberals' widespread failure to anticipate the Court's wariness of the mandate? Research conducted by University of Virginia psychologist Jonathan Haidt suggests one possible answer: Liberals just aren't as good as conservatives and libertarians at understanding how their opponents think. Haidt helped conduct research that asked respondents to fill out questionnaires about political narratives—first responding based on their own beliefs, but then responding as if trying to mimic the beliefs of their political opponents. "The results," he writes in the May issue of Reason, "were clear and consistent." Moderates and conservatives were the most able to think like their liberal political opponents. "Liberals," he reports, "were the least accurate, especially those who describe themselves as 'very liberal.'"

Liberals, on the other hand, have a different theory. The Court is just a bunch of partisan hacks who've bought into the most extreme ideas of the Republican base. Lithwick has argued that despite the law's self-evident constitutionality, the decision has "everything to do with optics, politics, and public opinion." Harvard law professor and former Solicitor General Charles Fried, who signed an amicus brief arguing in favor of the law, huffed that "the whole thing is just a canard that's been invented by the tea party and [anti-mandate legal architect] Randy Barnetts of the world, and I was astonished to hear it coming out of the mouths of the people on that bench."

The liberal position on the Court seems to be that as long as it accepts their arguments, it's an independent legal arbiter. But whenever it doesn't, it's a partisan political enforcer. The New Republic's Jonathan Cohn makes this explicit, arguing that it isn't just the health law that's on trial, but "the legitimacy of the Supreme Court."

So what now? To quote Lithwick: Optics, politics, and public opinion. Neera Tanden, a former administration health adviser and the president of the influential liberal organization the Center for American Progress, previewed the broader liberal response when she told The New York Times this week that "If this court overturns the individual mandate, it will galvanize Democrats to use the courts as a campaign issue….The idea that we would have gone through Bush v. Gore, Citizens United and now this."

Liberals never really took the legal arguments against ObamaCare seriously. But it turns out they are deeply concerned about the surrounding politics.

Peter Suderman is a senior editor at Reason magazine.