Ezra Klein has written a long piece for New Yorker that looks at the power of pure partisanship in U.S. politics through the example of the rapid and categorical rejection of an individual health care mandate by the conservatives and Republicans who invented it, and embraced it until very recently. For the most part, Ezra attributes this to the very human habit of “motivated reasoning,” in which group loyalties guide how we process information about this or that development or option.

It’s all very interesting, but what I found most striking about Ezra’s article was its reminder of how very rapidly the idea spread that the individual mandate might be unconstitutional, from the cranky to the partisan and eventually, it seems, right into the Supreme Court:

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….

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….”

How has this happened in just two years?

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.

I would add to this history the fact that few analysts thought there was any chance the Court would risk overturning the long line of previous decisions underlying Congress’ power to regulate interstate commerce, stretching back to the 1930s. But a couple of years of Tea Party-inspired “constitutional conservatism” encouraging a radical form of originalism clearly undermined the legitimacy of what had long been considered unassailable precedents. And so here we are.

Now perhaps the Supremes will surprise us all and uphold the mandate and banish the queasy sense I have that the bottom has dropped out and conservative radicalism, in Congress, in the think tanks, and even in the Courts, has no practical limit barring overwhelming electoral defeat. But the speed as much as the depth of the wave of amnesia–or “motivated reasoning,” if you wish–that has reversed so many prior positions on the Respectable Right will remain shocking even if it subsides on the Supreme Court steps.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.