The legal question is whether “use… by” a candidate can refer to ad time purchased on a candidate’s behalf by parties and joint fundraising committees. In the 4th Circuit case, two judges appointed by Democratic presidents ruled that the FCC’s interpretation of the law was wrong, and one judge appointed by a Republican president said the FCC got it right.

GOP has reason for optimism

A potential problem for Republicans is that the FCC position contradicts agency guidance from 1991 and a statement made to the Supreme Court last year by the Trump administration’s own solicitor general. In the recent Supreme Court case over spending limits, US Solicitor General John Sauer wrote in a filing that the “rules require broadcasters to charge low rates for candidate spending, but not for party spending—whether coordinated or independent.”

But Republicans have reason for optimism given the conservative makeup of the Supreme Court and the 4th Circuit dissent from Judge J. Harvie Wilkinson III, a Reagan appointee who argued that the FCC offered a “natural and plausible” interpretation of the law’s reference to “use… by” a candidate. The FCC welcomed the dissent, issuing a statement praising “Wilkinson’s sound and thoughtful analysis.”

Republicans further argue that courts have no jurisdiction yet because the FCC hasn’t made a “final” decision. The 4th Circuit judges decided they have jurisdiction because the FCC’s failure to act on a petition filed by Democratic candidates amounted to a “constructive denial.”

Wilkinson disagreed on that count, too, saying the FCC guidance is not a final order because the FCC is still reviewing the candidates’ application. If the Supreme Court does act quickly in the GOP’s favor, it could stay the 4th Circuit court mandate on the grounds that the FCC order isn’t final and can’t be appealed yet.

The Republican committees told the 4th Circuit to be wary of recent Supreme Court guidance. “Just two days ago, the Supreme Court reminded lower courts that they should not interfere with agency decision-making before it is final,” they wrote, referring to a ruling in Trump’s favor on vote-by-mail restrictions. “This Court should heed that instruction, and stay its order (or the mandate) pending a writ of certiorari to the Supreme Court.”