(Pablo Martinez Monsivais/AP)

When the Affordable Care Act became law two years ago, many legal observers wrote off the ensuing court challenges as quite frivolous, posing little substantive threat to the Obama administration’s signature legislative accomplishment.

After this week’s Supreme Court oral arguments, legal threats to the health reform law hardly look frivolous at all. Numerous Supreme Court experts could see the law being ruled unconstitutional. On InTrade, the odds are hovering around 60 percent. This all raises the question: Was there something legal experts missed?

Brad Joondeph is a law professor at Santa Clara University. In July 2010, he launched the ACA Litigation Blog, which has since traced every twist and turn in over two dozen lawsuits filed against the Affordable Care Act. All told, Joondeph has written hundreds of blog posts on the Affordable Care Act litigation. We spoke about how the cases developed, when they became a big threat to the law and what some observers might have missed. What follows is a lightly edited transcript of our conversation.

Sarah Kliff: Over the past two years, we’ve seen legal threats to the Affordable Care Act go from a really minor concern to an incredibly major one. I was hoping you could walk me through how, exactly, that happens. Was there something we all missed when these initial challenges were filed?

Brad Joondeph: I think that question implicates much larger questions about the meaning of the Constitution, and how that can change based on what people think it means. A lot of what goes on, in our understanding of the Constitution, is people fight about what is and isn’t a plausible understanding. And once enough people started talking about [the legal challenges] being a plausible interpretation, combined with it being so unpopular, momentum started to build.

At the beginning of anything in life, whether it’s a new social network page or a new legal idea, very few are willing to jump onto it. But when people do, it feeds into itself and snowballs. The arguments started to gain a measure of credibility that they lacked at the start.

Was there a certain moment when you started thinking, ‘Wow, these arguments are really gaining traction?’ Any particular turning point?

It was a gradual process. The most significant event though, I think, was the initial district court in Michigan that ruled against the law on its merits, and denied the United States’ motion to dismiss. I think the United States was taking the case seriously, but there was also a credible belief that every single complaint would be dismissed before even getting to the merits. If every lower court would have said, ‘This is so baseless that we’re not going to get past a motion to dismiss,’ no court of appeals would have ruled against the health-reform law.

And how did that ruling change how people viewed the health reform challenges?

As that was going on, a lot more academics were willing to support the idea. Politicians were becoming willing to put their names on amicus briefs. Then you had the Court of Appeals in the 11th Circuit rule against it. If that court had upheld the law as constitutional, you could have seen the Supreme Court deny cert. So I think it was a gradual process, where you saw more elite opinion getting behind the challenges. Opinions that matter to the Supreme Court started moving in that direction.

What kind of opinion tends to influence justices’ thinking? What are they looking at?

It’s fellow judges, particularly fellow judges who are similar ideologically. It’s also serious thinkers, public intellectuals and the legal academy. But it’s also, at some diffuse level, public opinion. We’re not here today if 80 percent of the public thinks the mandate is a great idea. You could, theoretically, imagine the same kind of arguments being made against Medicare. But the Supreme Court isn’t going to strike that down.

Can you think of other examples, from the Supreme Court’s history, where legal claims initially considered to be dubious ended up being taken quite seriously?

This did happen with the equal protection argument in Bush v. Gore. That was thrown in by [George W. Bush’s lawyer] Ted Olson. He reluctantly tacked it on, kind of an ‘everything in the kitchen sink’ approach. No one thought it was going anywhere, and they actually debated whether it was even worth including. Even at oral arguments, there didn’t seem to be much traction for oral arguments. But that’s what eventually won them the case. And there you have an argument that seemed just incredible, when first articulated, that ended up winning just three weeks later.

Looking back over the past two years, was there something we missed? Is there anything you see that, now, makes you think we should have realized this would become a big deal?

I think more than that, it’s a great example of how the Constitution sets very little in stone. It’s a broad framework that is set up for each generation to interpret. If this case were coming up in the 1960s, when the court had a very different conception of federal power, there’s no doubt it would have been upheld.

Nothing has changed in the wording of the Commerce Clause, but we have a different political regime, and we have a more conservative Democratic party. We’ve got a much more conservative Supreme Court than we did in the 1960s. This is a very broad and malleable framework, even though the words don’t change.

When you started tracking these lawsuits, how seriously did you think the legal challenges would be taken?

I’ve been trying to watch it objectively. Over time, I could see there was more buy-in. It was like, almost every month, it became more and more likely that the Supreme Court was going to find it a credible argument. Then you had Judge [Jeffrey Sutton, a Reagan appointee] and Judge [Laurence Silberman, a George W. Bush appointee] rule in favor of the law. Those were the first moments of push back in the other direction.

I thought those would have gotten more discussion than they did, but the court didn’t really seem to engage with those opinions. For me, watching this, it’s been a steady progression of a greater likelihood that this would go to the Supreme Court.