Update Sept. 22: Judge Nina Pillard will not recuse herself from the Clean Power Plan hearing, bringing the total number of judges to ten. Utility Dive's original primer follows.

Make no mistake, the Clean Power Plan is almost certainly heading for an ultimate showdown at the U.S. Supreme Court. The stakes are so high that virtually any lower court decision will be challenged.

But the U.S. Court of Appeals for the District of Columbia Circuit slated to consider the case first, with oral arguments beginning Sept. 27. So is that court's decision just a mere formality? Absolutely not, say experts.

The D.C. Circuit is widely regarded as the second most powerful court in the country, and its decisions stand when the Supreme Court is deadlocked or refuses to take a case. Given the high court's current eight-member status, the D.C. Circuit decision could take on even greater significance if the justices lock in a 4-4 tie over the federal carbon regulations.

Legal experts say that outcome is relatively unlikely, but it is not the only reason the D.C. Circuit decision will matter.

"The lower court decision sets up the case," said Ari Peskoe, senior fellow in electricity law at the Harvard Law School Environmental Law Program Policy Initiative. "The D.C. Circuit decision is going to be important regardless."

What's at stake is the Obama Administration's signature environmental initiative, a sweeping rule that aims to cut carbon emissions from the power sector 32% nationwide by 2030 from 2005 levels. It's also the engine behind the United States' commitment at the Paris climate talks. But critics say the carbon rules unfairly force operational coal plants offline, leading to a fierce backlash.

More than two dozen states, led by West Virginia Attorney General Patrick Morrisey, have challenged the rule, decrying a "war on coal" and what they say is federal regulatory overreach. In February, the Supreme Court put the rule on hold, halting formal implementation work until court challenges conclude. And in May, the D.C. Circuit took the unusual step of skipping the usual three-judge panel to evaluate the rule, instead agreeing to hear the case en banc, with all active and eligible judges taking part.

Since then, two judges have recused themselves. Chief Judge Merrick Garland will not weigh in, most likely because he is currently nominated to replace the late Supreme Court Justice Antonin Scalia. And Judge Nina Pillard “did not participate” in the court's en banc announcement, making it unlikely she will take part in the hearing.

Without Garland and Pillard, that leaves the court with nine judges who will hear Clean Power Plan arguments — five nominated by Democratic Presidents, and four by Republicans.

"That doesn’t mean they will rule for the EPA, but it’s as good a chance as you're gonna get," said Jim Rubin, a partner at Dorsey & Whitney LLP, where his practice focuses on climate change law and policy.

A unique hearing at the D.C. Circuit

The Circuit Court's decision to hear the case en banc was unexpected and highlights the significance of the Clean Power Plan arguments. Because any losing party before the usual three-judge panel was likely to apply for an en banc review, the decision likely means the case will head to the Supreme Court faster. But it has also complicated the strategy attorneys may employ.

"In a normal circuit case, you can spend more time gaming it," said Rubin. "With three judges you could try and model your arguments, but now you have all the judges throwing questions at you. It is certainly hard to look at it collectively."

He noted that the court has scheduled a second day for arguments on Sept. 28, anticipating the complexity of the case.

"This is an unusual, almost unique circumstance," Rubin said. "It's going to be a long argument, with a lot of complex issues. The judges will be well-versed."

The full panel of 11 active circuit court judges would likely have been more favorable to the EPA — Garland is a Clinton appointee, and Pillard was tapped by Obama. So while the court might appear to lean toward the EPA's case on paper, there is some benefit to challengers with the en banc review.

Similarly, the original three-judge panel scheduled to hear the case would have been more likely to find for the EPA, Rubin said. Now, "you opponents just have to convince five judges."

That first panel included circuit judges Karen LeCraft Henderson, Judith Ann Wilson Rogers and Srikanth Srinivasan who denied the states' appeal to stay the rule, before the Supreme Court weighed in. Rogers was nominated by Clinton, and Srinivasan by Obama.

Agency authority and judicial deference

Since the Clean Power Plan was first proposed, low-priced natural gas and renewable energy have put most states within reach of their 2030 goals. But challengers say their case goes beyond the ability to meet the targets, seeking to prevent undue federal control over state power planning authority.

That likely means much of the court's time will be spent discussing whether or not the U.S. Environmental Protection Agency has the authority to regulate emissions from existing plants, under section 111(d) of the Clean Air Act.

According to the EPA, the law identifies specific factors regulators must consider in establishing emission guidelines, but said it properly applied those factors and the Supreme Court has previously confirmed the agency has the authority to regulate emissions.

The states, however, counter in their reply brief that EPA’s "novel contention that it may require emission reductions premised on altering the nation’s mix of electric generation ... cannot stand because EPA has not shown clear congressional authorization." They also argue that the agency cannot regulate CO2 under section 111(d) because other power plant emissions are regulated under Section 112.

While EPA acknowledges in its brief that Section 111(d) is "ambiguous," the result of conflicting Congressional mandates in the House and Senate that date to 1990, the agency said it "reasonably resolved those ambiguities — and avoided creating an unnecessary conflict in enacted statutory text — by concluding that Congress did not intend to bar regulation of different pollutants under different programs."

"That probably will be the most critical argument back and forth," Rubin said, adding "there are a number of state-specific and industry-specific points that will be made, to the extent there is time."

Peskoe said it's "always interesting to see what issues the judges key in on," but he noted that the largest chunk of time, 35 minutes, has been set aside to discussions of EPA's authority.

"Within any of these issues there are all sorts of sub-points," he said. "Sometimes oral arguments are really just the justices discussing the case among themselves."

If the case follows a similar narrative to the Mercury and Air Toxics Standards (MATS), the question of EPA's authority is likely to loom large. Last year, the Supreme Court ruled the agency had exceeded its authority in crafting MATS because it did not factor in potential costs in an initial finding that the rule was necessary.

Though EPA was permitted, through a subsequent D.C. Circuit decision, to make changes to the rule without throwing it out, the Supreme Court ruling was seen by many energy lawyers as an indication that justices are becoming increasingly skeptical of granting deference to federal agencies on their interpretations of the law.

That skepticism of what's known as "Chevron deference," after a 1984 Supreme Court case, could bode poorly for the EPA if and when the Clean Power Plan reaches the high court.

"I can’t imagine someone not appealing this," said Rubin. "EPA’s big national rules tend to find their way to the Supreme Court."

Peskoe said there are scenarios where an appeal by the administration is unlikely, but they would hinge election outcomes. For instance, if Donald Trump wins the presidency and the Clean Power Plan is struck down, it becomes less likely the government would appeal. But Hillary Clinton would almost certainly appeal a loss of Obama's environmental rules.

If the court finds in favor of the EPA, states and industry will almost certainly challenge in the high court.

The real question is what will happen after a challenge. "There's a lot of uncertainty at the Supreme Court," said Peskoe. While an 8-member court could decide the case, it is also possible the Supreme Court could accept the review and then put it on hold until the ninth seat was filled.

Circuit decisions have been taking up to six months to write in recent years, Peskoe added, and it's not clear what an en banc review will do to that timeframe. That means a decision won't come until after the election, but possibly before a new Supreme Court justice has been confirmed.

See Also: Why insiders think the EPA got the best of the Clean Power Plan hearing last week

Get to know the judges

Of the nine active judges who will hear the case, the 5-4 nominating split is the important statistic. Clinton nominated two of them, and Obama three; President George W. Bush nominated three, and his father President George H.W. Bush nominated just one.

But there are other fun stats: Two of the judges are foreign born — Thomas Beall Griffith in Yokohama, Japan, and Srikanth Srinivasan in Chandigarh, India. Two were born in Washington, D.C., where the arguments will take place. Judge Karen LeCraft Henderson took over Ken Starr's seat, who was independent counsel investigating scandals from Bill Clinton's tenure.

Perhaps more useful, some of the judges have already weighed in on high-profile energy cases.

The court's decision to uphold the Mercury and Air Toxics Standards rule had Garland (recused) in favor of it, along with Judge Judith Ann Wilson Rogers. Judge Brett M. Kavanaugh opposed the rule. The second MATS ruling, allowing the rule to stand while the EPA made changes to it, had all three on the same side, supporting the EPA's case.

In an earlier decision to delay a stay of implementation of the Clean Power Plan, Srinivasan, Rogers, and Judge Karen Henderson all sided with the federal agency against the stay, only to be overruled by the high court.

The decision to vacate FERC Order 745, governing demand response in wholesale markets, involved the senior judges who will not hear CPP arguments, and Judge Janice Rogers Brown, who sided with the generation industry, against the federal agency.

In the court's decision in 2012 to reject the White House's Cross-State Air Pollution Rule, Rogers sided with the EPA.

For more information on the nine judges likely to hear the Clean Power Plan case, see the biographies below.

Karen LeCraft Henderson Born 1944 in Oberlin, OH Education:

Duke University, B.A., 1966

University of North Carolina School of Law, J.D., 1969 Nominated by George H.W. Bush on May 8, 1990, to a seat vacated by Kenneth W. Starr. Confirmed by the Senate on June 28, 1990, and received commission on July 5, 1990. One of the original three judges assigned to hear Clean Power Plan arguments, before the case was expanded. She refused to stay implementation of the rule before that decision was undone by the Supreme Court. Learn More >>

Judith Ann Wilson Rogers Born 1939 in New York, NY Education:

Radcliffe College, A.B., 1961

Harvard Law School, LL.B., 1964

University of Virginia School of Law, LL.M., 1988 Nominated by William J. Clinton on November 17, 1993, to a seat vacated by Clarence Thomas. Confirmed by the Senate on March 10, 1994, and received commission on March 11, 1994. One of the original three judges assigned to hear Clean Power Plan arguments, before the case was expanded. She refused to stay implementation of the rule before that decision was undone by the Supreme Court. Rogers sided with the EPA in upholding the Mercury and Air Toxics Standards rule, along with Chief Judge Merrick Garland. She also sided with the EPA on the Cross-State Air Pollution Rule in 2012, as well as in 2015. Also, recently found the Federal Energy Regulatory Commission does not have to examine upstream impacts when approving liquefied natural gas export licenses. Learn More >>

David S. Tatel Born 1942 in Washington, DC Nominated by William J. Clinton on June 20, 1994, to a seat vacated by Ruth Bader Ginsburg. Confirmed by the Senate on October 6, 1994, and received commission on October 7, 1994. Education:

University of Michigan, B.A., 1963

University of Chicago Law School, J.D., 1966 In 2012 Tatel sided with the federal government in Coalition for Responsible Regulation v. EPA, refusing to overturn the Climate Pollution Endangerment Finding, the Clean Car Standards and the Carbon Pollution Limits for Big New Power Plants and Industrial Sources (know as the timing and tailoring rules). Learn More >>

Janice Rogers Brown Born 1949 in Greenville, AL Nominated by George W. Bush on February 14, 2005, to a seat vacated by Stephen F. Williams. Confirmed by the Senate on June 8, 2005, and received commission on June 10, 2005. Education:

California State University, Sacramento, B.A., 1974

University of California, Los Angeles, School of Law, J.D., 1977

University of Virginia School of Law, LL.M., 2004 Brown sided with the generation industry in vacating FERC Order 745, governing demand response in wholesale markets, and wrote the order for the majority. In that decision, she wrote: "Because FERC’s rule entails direct regulation of the retail market—a matter exclusively within state control—it exceeds the Commission’s authority." Learn More >>

Thomas Beall Griffith Born 1954 in Yokohama, Japan Nominated by George W. Bush on February 14, 2005, to a seat vacated by Patricia M. Wald. Confirmed by the Senate on June 14, 2005, and received commission on June 29, 2005. Education:

Brigham Young University, B.A., 1978

University of Virginia School of Law, J.D., 1985 Griffith joined with Kavanaugh in overturning the Cross-State Air Pollution Rule in 2012, and also rejected arguments that would have vacated the Cross-State Air Pollution Rule in 2015. Also, recently found the Federal Energy Regulatory Commission does not have to examine upstream impacts when approving liquefied natural gas export licenses. Learn More >>

Brett M. Kavanaugh Born 1965 in Washington, D.C. Federal Judicial Service:

Nominated by George W. Bush on January 25, 2006, to a seat vacated by Laurence H. Silberman. Confirmed by the Senate on May 26, 2006, and received commission on May 30, 2006. Education:

Yale College, B.A., 1987

Yale Law School, J.D., 1990 Kavanaugh sided with industry in the Mercury and Air Toxics Standards ruling, though his dissent was overruled by Chief Judge Merrick Garland and Judge Judith Ann Wilson Rogers. He wrote the opinion for the court when the Circuit overturned the Cross-State Air Pollution Rule in 2012, but Kavanaugh rejected arguments that would have vacated the CSAPR when it was back in the court in 2015. Learn More >>

Srikanth Srinivasan Born 1967 in Chandigarh, India Federal Judicial Service:

Nominated by Barack Obama on January 4, 2013, to a seat vacated by Arthur Raymond Randolph. Confirmed by the Senate on May 23, 2013, and received commission on May 24, 2013. Education:

Stanford University, B.A., 1989

Stanford Law School, J.D., 1995

Stanford Graduate School of Business, M.B.A., 1995 One of the original three judges assigned to hear Clean Power Plan arguments, before the case was expanded. Srinivasan refused to stay implementation of the rule before that decision was undone by the Supreme Court. Learn More >>

Patricia Ann Millett Born 1963 in Dexter, ME Federal Judicial Service:

Nominated by Barack Obama on June 4, 2013, to a seat vacated by John Glover Roberts, Jr. Confirmed by the Senate on December 10, 2013, and received commission on December 10, 2013. Education:

University of Illinois, B.A., 1985

Harvard Law School, J.D., 1988 Sided with environmentalists opposed to the Cape Wind project, finding that the federal government violated the National Environmental Policy Act by granting a lease to the project. Also, recently found the Federal Energy Regulatory Commission does not have to examine upstream impacts when approving liquefied natural gas export licenses. Learn More >>

Robert Leon Wilkins Born 1963 in Muncie, IN Nominated by Barack Obama on June 4, 2013, to a seat vacated by David Bryan Sentelle. Confirmed by the Senate on January 13, 2014, and received commission on January 15, 2014. Education:

Rose-Hulman Institute of Technology, B.S., 1986

Harvard Law School, J.D., 1989 Sided with environmentalists opposed to the Cape Wind project, finding that the federal government violated the National Environmental Policy Act by granting a lease to the project. Learn More >>

Correction: An earlier version of this post mistakenly attributed a passage from Judge Harry Edwards's dissent in the FERC Order 745 case to Judge Janice Rodgers Brown.