You probably thought that last week’s only notable debate was the one between Hillary Clinton and Donald Trump at Hofstra University, but, on Tuesday, supporters and opponents of EPA’s Clean Power Plan had a high-stakes showdown of their own in Washington, D.C.: a seven-hour oral argument before the D.C. Circuit Court of Appeals. The proceedings may not have spawned an SNL sketch, but in the wonky world of environmental law, they were a very big deal.

“Everyone will be there,” my colleague wrote a few days before the hearing, explaining why it was totally worth it to give up my ticket to see Adele at Madison Square Garden and instead take a train to Washington so I could line up at 6:00 a.m. to get into a courtroom.

And everyone (except Adele) was there: politicians and activists, academics and journalists, lobbyists and executives, the people who lobbyists and executives pay to stand in line for them so they can sleep in (actually a thing), a guy driving a truck with a burning constitution painted on it, a ton of lawyers, and, most importantly, 10 of the nation’s fanciest judges.

Truck with burning constitution.

If you think that sounds like a lot of judicial firepower for a single hearing, you’re right. Typically, cases before the D.C. Circuit are heard by a three-judge panel, at least initially. But, for this suit, the court took the very unusual step of skipping straight to en banc review, which means that all of the circuit’s active judges get a say in the outcome — except Chief Judge Merrick Garland, who has recused himself from D.C. Circuit matters while his nomination to the Supreme Court is pending. (Remember that time the president nominated someone to the Supreme Court and Senate Republicans refused to give him a confirmation hearing? He’s still waiting.)

The basics

Before diving into the details of the argument, a refresher on the rule at issue: “Clean Power Plan” is EPA’s shorthand for a set of federal guidelines, issued under the Clean Air Act, that limit carbon dioxide emissions from the nation’s existing (as opposed to newly constructed) power plants. Based on these guidelines, states are expected (but not required) to design customized compliance plans for plants within their borders. If a state declines to submit a plan, EPA will step in to regulate that state’s plants directly.

By 2030, the Clean Power Plan is projected to reduce the power sector’s carbon emissions to 32 percent below 2005 levels. This is slightly less impressive than it sounds, because the sector already emits 21 percent less carbon than it did in 2005, meaning it’s already two-thirds of the way to compliance. Nevertheless, the plan is widely regarded as the most important environmental initiative of the Obama presidency.