The appeals court’s order Thursday sets aside an Aug. 31 ruling by a three-judge panel that rejected the House’s effort to subpoena McGahn and gutted the House’s historically broad subpoena power. The judges called for new briefs in the matter to be filed beginning next month and running through mid-January, shortly before Inauguration Day.

The timetable ensures that it will be nearly two years from the time Democrats first subpoenaed McGahn — in April 2019 — and when they might receive a final ruling on the matter. Even a favorable ruling from the full appeals court could be appealed to the Supreme Court, leaving House Democrats without resolution well into 2021.

McGahn testified repeatedly to Mueller’s team about efforts by Trump to curb or end the Mueller probe. He provided testimony that Trump twice ordered him to fire Mueller and once asked him to create a false record about the effort. McGahn and his deputy, Annie Donaldson, also shared notes with Mueller that captured some of the frantic West Wing maneuvering in response to the Mueller probe.

After Mueller’s report was made public in April 2019, House investigators, led by the Judiciary Committee, sought to reconstruct some of Mueller’s evidence, seeking testimony from McGahn, underlying documents held by the Justice Department and grand jury information that was redacted in the final special counsel report. All of their efforts have been locked up in legal proceedings since.

Democrats pointed to the slow crawl of their legal battles to justify impeaching Trump last year for obstructing congressional investigations. Speaker Nancy Pelosi has also thrown her support behind legislation that would prioritize congressional subpoena enforcement in the courts. The GOP-controlled Senate acquitted Trump during his impeachment trial.

The appeals judges who will consider the McGahn case early next year include seven Democratic appointees and two Republican appointees. There are four active GOP appointees on the D.C. Circuit, but two of Trump’s appointees — Judges Greg Katsas and Neomi Rao — have recused themselves from the McGahn case.

It will be the second trip by the McGahn case to the full bench of the D.C. Circuit, which rarely sits en banc.

After a district court judge upheld the House Judiciary Committee subpoena to the former White House counsel in November 2019 — albeit without addressing which specific questions McGahn would have to answer — a divided D.C. Circuit panel ruled in February that under the Constitution courts should have no role in adjudicating subpoena fights between the executive and legislative branches.

The full bench of the D.C. Circuit agreed to take up that issue at the House’s request and reached the opposite conclusionin a 7-2 decision rendered in August that found such disputes amenable to resolution by the courts. However, that ruling left open some other legal issues, including whether there was any specific legal mechanism open to the House to enforce its subpoenas in court.

All the court rulings leave open some ways for the House to enforce subpoenas, but through means that are often impractical or unpalatable to lawmakers. The Justice Department could prosecute someone who defies a subpoena for contempt, but as a matter of policy will not do so when that person is a current or former executive branch official following a directive from the president to assert executive privilege.

The House also has a so-called inherent contempt power to use its own officers to arrest or fine those who don’t comply with a subpoena, but it has been rarely used.