It’s arguably the most important single hour of federal policymaking this year, and it’s happening Wednesday morning inside a government building on Capitol Hill. But except for clusters of reporters and attorneys, joined by a few dozen citizens who’ve waited hours in a long queue for a glimpse, the event will remain invisible forever.

The occasion is the Supreme Court oral argument, starting at 10 a.m., in a case threatening the viability of the 2010 Affordable Care Act. The justices are going to decide if one phrase fails to legally underpin one of the statute’s central provisions: Tax breaks for poor and middle-income Americans who obtain medical insurance through the federal government’s new online marketplace.

King v. Burwell is one of this term’s landmark disputes, along with the cases that could establish a constitutional right for gay couples to marry, to be argued this spring. Health care for millions is threatened in the first instance, and the civil rights of millions is at stake in the other. But taxpayers whose futures hang in the balance will never get to witness their government in action at this important juncture.

That’s because the Supreme Court has never allowed television cameras to record the only portion of its deliberative process ever open to the public. And both slim swirls of momentum that seemed to be forming behind a reversal in that policy, inside the court and in Congress, have quietly but undeniably dissipated.

The two junior justices, Elena Kagan and Sonia Sotomayor, both testified during their Senate confirmation hearings at the end of the last decade that they favored opening oral arguments to TV coverage. For those who advocate for sunshine as democracy’s best disinfectant, there was real hope that once on the court they’d convince their new colleagues to go along — especially because a majority of justices now are baby boomers reared in the TV age.

Instead, the opposite has happened. No other justice has come out in favor of cameras in court, and just in the last month both of President Barack Obama’s nominees declared they were on course to reverse their positions.

Kagan told a University of Chicago audience that, since the court operates well now, she’s joined those justices who are “are appropriately wary of anything that might upset the dynamic of the institution.” Sotomayor, in an appearance in Florida, cited the more pervasive argument. “I think the temptation to grandstand in front of a camera is so huge,” she said when asked about broadcasting arguments. “I am moving more closely to saying I think it might be a bad idea.”

A year ago, she had a more paternalistic rationale for her intensifying case of videophobia. The meaning of the give-and-take among the justices and the lawyers, she said on PBS, would go right over the heads of most viewers, so it might be pointless to give the public an opportunity to try to understand.

There are ready rebuttals for all those arguments. TV cameras introduced into many lower federal courts haven’t upended their dynamics, nor have they prompted many litigants and judges to play to the cameras. Most people who chose to sit through 60 minutes of rapid-fire jousting in legalistic shorthand would appreciate what’s going on — or else be fully aware they couldn’t, but satisfy some curiosity anyway. Those who saw only snippets on the news would be reminded constantly that oral arguments aren’t great predictors of a case’s outcome. And beside all that, members of the public have a right to look in when public business is being conducted — even when they may misunderstand what they’re looking at.

All the same arguments infused the debates over whether Congress should be televised. (Broadcasts of House proceedings began 36 years ago this month, and the Senate has been on the air almost 29 years.) There’s still disagreement about whether the public has come to a better understanding of how the legislative process works, and whether the gavel-to-gavel coverage has exacerbated or mitigated the coarsening of legislative discourse and the use of the chambers as sound stages for campaign rhetoric and de facto fundraising appeals. But it’s essentially impossible to find a lawmaker in favor of making C-SPAN go dark.

Still, concerns about separation of powers have tamped down rumblings on the Hill about making the Supreme Court be more like Congress. Just seven Democrats and three Republicans have signed on to a pair of House bills to push the court to allow filming at public sessions. Senate Judiciary Chairman Charles E. Grassley, R-Iowa, has promised to write such a measure, but only five of the 15 senators on that panel remain from a somewhat sustained push for a measure six years ago.

Fix the Court, a new advocacy group, hopes to jump-start interest by spending about $50,000 this week airing a 30-second spot on some cable news shows. “America’s biggest moments wouldn’t be the same without TV, but the biggest decisions still happen in the dark, behind closed doors,” the announcer says. “It’s time for us to see the history made here, in the light of day.”

Chief Justice John G. Roberts Jr., in his annual report to Congress at the end of 2014, discussed his colleagues’ snail-like approach to new information technology, noting that “courts will always be prudent whenever it comes to embracing the ‘next big thing.’” He didn’t even hint at permitting smartphones for live tweeting or Snapchatting inside the courtroom — which arguably fit that definition in our social media era. In fact, he didn’t even mention TV.

Instead, he talked about how pneumatic tubes were cutting edge in the late 1800s but weren’t used by the justices for sharing paperwork until the 1930s.

And radio? For the past five years, the court has made public its audio recordings of arguments — but, with a handful of exceptions, they’re released several days afterward. So, to hear every word spoken in the Obamacare case, tune in Friday.

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