On March 23, 2010, the day that President Obama signed the Affordable Care Act into law, fourteen state attorneys general filed suit against the law’s requirement that most Americans purchase health insurance, on the ground that it was unconstitutional. It was hard to find a law professor in the country who took them seriously. “The argument about constitutionality is, if not frivolous, close to it,” Sanford Levinson, a University of Texas law-school professor, told the McClatchy newspapers. Erwin Chemerinsky, the dean of the law school at the University of California at Irvine, told the Times, “There is no case law, post 1937, that would support an individual’s right not to buy health care if the government wants to mandate it.” Orin Kerr, a George Washington University professor who had clerked for Justice Anthony Kennedy, said, “There is a less than one-per-cent chance that the courts will invalidate the individual mandate.” Today, as the Supreme Court prepares to hand down its decision on the law, Kerr puts the chance that it will overturn the mandate—almost certainly on a party-line vote—at closer to “fifty-fifty.” The Republicans have made the individual mandate the element most likely to undo the President’s health-care law. The irony is that the Democrats adopted it in the first place because they thought that it would help them secure conservative support. It had, after all, been at the heart of Republican health-care reforms for two decades.

Republicans turned against the individual mandate after supporting it for two decades. Illustration by Nishant Choksi

The mandate made its political début in a 1989 Heritage Foundation brief titled “Assuring Affordable Health Care for All Americans,” as a counterpoint to the single-payer system and the employer mandate, which were favored in Democratic circles. In the brief, Stuart Butler, the foundation’s health-care expert, argued, “Many states now require passengers in automobiles to wear seat-belts for their own protection. Many others require anybody driving a car to have liability insurance. But neither the federal government nor any state requires all households to protect themselves from the potentially catastrophic costs of a serious accident or illness. Under the Heritage plan, there would be such a requirement.” The mandate made its first legislative appearance in 1993, in the Health Equity and Access Reform Today Act—the Republicans’ alternative to President Clinton’s health-reform bill—which was sponsored by John Chafee, of Rhode Island, and co-sponsored by eighteen Republicans, including Bob Dole, who was then the Senate Minority Leader.

After the Clinton bill, which called for an employer mandate, failed, Democrats came to recognize the opportunity that the Chafee bill had presented. In “The System,” David Broder and Haynes Johnson’s history of the health-care wars of the nineties, Bill Clinton concedes that it was the best chance he had of reaching a bipartisan compromise. “It should have been right then, or the day after they presented their bill, where I should have tried to have a direct understanding with Dole,” he said.

Ten years later, Senator Ron Wyden, an Oregon Democrat, began picking his way back through the history—he read “The System” four times—and he, too, came to focus on the Chafee bill. He began building a proposal around the individual mandate, and tested it out on both Democrats and Republicans. “Between 2004 and 2008, I saw over eighty members of the Senate, and there were very few who objected,” Wyden says. In December, 2006, he unveiled the Healthy Americans Act. In May, 2007, Bob Bennett, a Utah Republican, who had been a sponsor of the Chafee bill, joined him. Wyden-Bennett was eventually co-sponsored by eleven Republicans and nine Democrats, receiving more bipartisan support than any universal health-care proposal in the history of the Senate. It even caught the eye of the Republican Presidential aspirants. In a June, 2009, interview on “Meet the Press,” Mitt Romney, who, as governor of Massachusetts, had signed a universal health-care bill with an individual mandate, said that Wyden-Bennett was a plan “that a number of Republicans think is a very good health-care plan—one that we support.”

Wyden’s bill was part of a broader trend of Democrats endorsing the individual mandate in their own proposals. John Edwards and Hillary Clinton both built a mandate into their campaign health-care proposals. In 2008, Senator Ted Kennedy brought John McDonough, a liberal advocate of the Massachusetts plan, to Washington to help with health-care reform. That same year, Max Baucus, the chairman of the Senate Finance Committee, included an individual mandate in the first draft of his health-care bill. The main Democratic holdout was Senator Barack Obama. But by July, 2009, President Obama had changed his mind. “I was opposed to this idea because my general attitude was the reason people don’t have health insurance is not because they don’t want it. It’s because they can’t afford it,” he told CBS News. “I am now in favor of some sort of individual mandate.”

This process led, eventually, to the Patient Protection and Affordable Care Act—better known as Obamacare—which also included an individual mandate. But, as that bill came closer to passing, Republicans began coalescing around the mandate, which polling showed to be one of the legislation’s least popular elements. In December, 2009, in a vote on the bill, every Senate Republican voted to call the individual mandate “unconstitutional.”

This shift—Democrats lining up behind the Republican-crafted mandate, and Republicans declaring it not just inappropriate policy but contrary to the wishes of the Founders—shocked Wyden. “I would characterize the Washington, D.C., relationship with the individual mandate as truly schizophrenic,” he said.

It was not an isolated case. In 2007, both Newt Gingrich and John McCain wanted a cap-and-trade program in order to reduce carbon emissions. Today, neither they nor any other leading Republicans support cap-and-trade. In 2008, the Bush Administration proposed, pushed, and signed the Economic Stimulus Act, a deficit-financed tax cut designed to boost the flagging economy. Today, few Republicans admit that a deficit-financed stimulus can work. Indeed, with the exception of raising taxes on the rich, virtually every major policy currently associated with the Obama Administration was, within the past decade, a Republican idea in good standing.

Jonathan Haidt, a professor of psychology at New York University’s business school, argues in a new book, “The Righteous Mind,” that to understand human beings, and their politics, you need to understand that we are descended from ancestors who would not have survived if they hadn’t been very good at belonging to groups. He writes that “our minds contain a variety of mental mechanisms that make us adept at promoting our group’s interests, in competition with other groups. We are not saints, but we are sometimes good team players.”

One of those mechanisms is figuring out how to believe what the group believes. Haidt sees the role that reason plays as akin to the job of the White House press secretary. He writes, “No matter how bad the policy, the secretary will find some way to praise or defend it. Sometimes you’ll hear an awkward pause as the secretary searches for the right words, but what you’ll never hear is: ‘Hey, that’s a great point! Maybe we should rethink this policy.’ Press secretaries can’t say that because they have no power to make or revise policy. They’re told what the policy is, and their job is to find evidence and arguments that will justify the policy to the public.” For that reason, Haidt told me, “once group loyalties are engaged, you can’t change people’s minds by utterly refuting their arguments. Thinking is mostly just rationalization, mostly just a search for supporting evidence.”

Psychologists have a term for this: “motivated reasoning,” which Dan Kahan, a professor of law and psychology at Yale, defines as “when a person is conforming their assessments of information to some interest or goal that is independent of accuracy”—an interest or goal such as remaining a well-regarded member of his political party, or winning the next election, or even just winning an argument. Geoffrey Cohen, a professor of psychology at Stanford, has shown how motivated reasoning can drive even the opinions of engaged partisans. In 2003, when he was an assistant professor at Yale, Cohen asked a group of undergraduates, who had previously described their political views as either very liberal or very conservative, to participate in a test to study, they were told, their “memory of everyday current events.”

The students were shown two articles: one was a generic news story; the other described a proposed welfare policy. The first article was a decoy; it was the students’ reactions to the second that interested Cohen. He was actually testing whether party identifications influence voters when they evaluate new policies. To find out, he produced multiple versions of the welfare article. Some students read about a program that was extremely generous—more generous, in fact, than any welfare policy that has ever existed in the United States—while others were presented with a very stingy proposal. But there was a twist: some versions of the article about the generous proposal portrayed it as being endorsed by Republican Party leaders; and some versions of the article about the meagre program described it as having Democratic support. The results showed that, “for both liberal and conservative participants, the effect of reference group information overrode that of policy content. If their party endorsed it, liberals supported even a harsh welfare program, and conservatives supported even a lavish one.”

In a subsequent study involving just self-described liberal students, Cohen gave half the group news stories that had accompanying Democratic endorsements and the other half news stories that did not. The students who didn’t get the endorsements preferred a more generous program. When they did get the endorsements, they went with their party, even if this meant embracing a meaner option.

This kind of thinking is, according to psychologists, unsurprising. Each of us can have firsthand knowledge of just a small number of topics—our jobs, our studies, our personal experiences. But as citizens—and as elected officials—we are routinely asked to make judgments on issues as diverse and as complex as the Iranian nuclear program, the environmental impact of an international oil pipeline, and the likely outcomes of branding China a “currency manipulator.”

According to the political-science literature, one of the key roles that political parties play is helping us navigate these decisions. In theory, we join parties because they share our values and our goals—values and goals that may have been passed on to us by the most important groups in our lives, such as our families and our communities—and so we trust that their policy judgments will match the ones we would come up with if we had unlimited time to study the issues. But parties, though based on a set of principles, aren’t disinterested teachers in search of truth. They’re organized groups looking to increase their power. Or, as the psychologists would put it, their reasoning may be motivated by something other than accuracy. And you can see the results among voters who pay the closest attention to the issues.

In a 2006 paper, “It Feels Like We’re Thinking,” the political scientists Christopher Achen and Larry Bartels looked at a National Election Study, a poll supported by the National Science Foundation, from 1996. One of the questions asked whether “the size of the yearly budget deficit increased, decreased, or stayed about the same during Clinton’s time as President.” The correct answer is that it decreased, dramatically. Achen and Bartels categorize the respondents according to how politically informed they were. Among the least-informed respondents, Democrats and Republicans picked the wrong answer in roughly equal numbers. But among better-informed voters the story was different. Republicans who were in the fiftieth percentile gave the right answer more often than those in the ninety-fifth percentile. Bartels found a similar effect in a previous survey, in which well-informed Democrats were asked whether inflation had gone down during Ronald Reagan’s Presidency. It had, but many of those Democrats said that it hadn’t. The more information people had, it seemed, the better they were at arranging it to fit what they wanted to believe. As Bartels told me, “If I’m a Republican and an enthusiastic supporter of lower tax rates, it is uncomfortable to recognize that President Obama has reduced most Americans’ taxes—and I can find plenty of conservative information sources that deny or ignore the fact that he has.”

Recently, Bartels noticed a similar polarization in attitudes toward the health-care law and the Supreme Court. Using YouGov polling data, he found that less-informed voters who supported the law and less-informed voters who opposed it were equally likely to say that “the Supreme Court should be able to throw out any law it finds unconstitutional.” But, among better-informed voters, those who opposed the law were thirty per cent more likely than those who supported it to cede that power to the Court. In other words, well-informed opponents realized that they needed an activist Supreme Court that was willing to aggressively overturn laws if they were to have any hope of invalidating the Affordable Care Act.

Orin Kerr says that, in the two years since he gave the individual mandate only a one-per-cent chance of being overturned, three key things have happened. First, congressional Republicans made the argument against the mandate a Republican position. Then it became a standard conservative-media position. “That legitimized the argument in a way we haven’t really seen before,” Kerr said. “We haven’t seen the media pick up a legal argument and make the argument mainstream by virtue of media coverage.” Finally, he says, “there were two conservative district judges who agreed with the argument, largely echoing the Republican position and the media coverage. And, once you had all that, it really became a ballgame.”

Jack Balkin, a Yale law professor, agrees. “Once Republican politicians say this is unconstitutional, it gets repeated endlessly in the partisan media that’s friendly to the Republican Party”—Fox News, conservative talk radio, and the like—“and, because this is now the Republican Party’s position, the mainstream media needs to repeatedly explain the claims to their readers. That further moves the arguments from off the wall to on the wall, because, if you’re reading articles in the Times describing the case against the mandate, you assume this is a live controversy.” Of course, Balkin says, “if the courts didn’t buy this, it wouldn’t get anywhere.”

But the courts are not as distant from the political process as some like to think. The first judge to rule against the individual mandate was Judge Henry Hudson, of Virginia’s Eastern District Court. Hudson was heavily invested in a Republican consulting firm called Campaign Solutions, Inc. The company had worked with the Presidential campaigns of John McCain and George W. Bush, the Republican National Committee, the Swift Boat Veterans for Truth, and Ken Cuccinelli—the Virginia state attorney general who is one of the plaintiffs in the lawsuits against the Affordable Care Act.

The fact that a judge—even a partisan judge in a district court—had ruled that a central piece of a Democratic President’s signature legislative accomplishment was unconstitutional led the news across the country. Hudson’s ruling was followed by a similar, and even more sweeping, ruling, by Judge Roger Vinson, of the Northern District of Florida. Vinson declared the entire bill unconstitutional, setting off a new round of stories. The twin rulings gave conservatives who wanted to believe that the mandate was unconstitutional more reason to hold that belief. Voters who hadn’t thought much about it now heard that judges were ruling against the Administration. Vinson and Hudson were outnumbered by other district judges who either upheld the law or threw out lawsuits against it, but those rulings were mostly ignored.