“The idea that a president and his current and former advisors enjoy absolute immunity from subpoena — particularly during impeachment proceedings — finds no support in early American practice,” the GOP ex-officials contend. “During the early republic, Congresses and presidents recognized that Congress had nearly untrammeled authority to request documents and testimony to support impeachment proceedings.”

Signed on to the brief are several prominent former lawmakers, including former Sen. Gordon Humphrey (R-N.H.), and ex-Reps. Mickey Edwards (R-Okla.) and Jim Leach (R-Iowa). Former Justice Department official Stuart Gerson and prominent conservative lawyer George Conway are also among those asking the D.C. Circuit Court of Appeals to endorse Congress’s right to question senior executive branch officials about potential misconduct.

“Placing the president and his aides above the law would be truly un-American. Early U.S. Congresses and courts subpoenaed presidents, and the presidents complied with those subpoenas. That should remain the case today,” said another signer, former Rep. Reid Ribble (R-Wis.).

With many originalist judges and legal scholars fond of approaching the Constitution with their best approximation of an 18th-century eye, the brief cites various examples from the late 1700s and early 1800s that the ex-officials contend show the founders favored Congress enjoying robust access to executive branch secrets.

The brief notes that in 1794, America’s first president, George Washington, rejected a House request for documents about negotiations aimed at signing a peace treaty with England. However, Washington specifically noted that he was refusing the demand because it did not involve a call for impeachment.

The friend-of-the-court submission also points out that as early as 1807, the Supreme Court ruled that the president should not be thought of as a “king,” with complete immunity from the legal process. The former officials argue that such logic means the president’s advisers also lack any power to completely rebuff congressional inquiries.

The brief was prepared by Protect Democracy, which describes itself as an anti-authoritarian watchdog group set up after Trump’s election in 2016, to maintain “guardrails” in the American political system. The lead counsel listed on the filing is the group’s legal director, Justin Florence, who worked in the White House counsel’s office under President Barack Obama.

The Trump administration maintains that its claim of absolute testimonial immunity for McGahn is not an unusual one. A Justice Department opinion written during the Obama administration notes such a stance as far back as the Nixon era.

However, in 2008, a district court judge turned down the Justice Department’s claim of absolute immunity for a former White House counsel to President George W. Bush, Harriet Miers. The case was settled without an appeals court ruling that might have set a clear precedent.

Three D.C. Circuit judges, Karen Henderson, Judith Rogers and Thomas Griffith, are scheduled to hear arguments in the McGahn case on Jan. 3. The panel leans conservative. Henderson is an appointee of President George H.W. Bush. Rogers was appointed by President Bill Clinton. Griffith is an appointee of President George W. Bush.

The case is on an accelerated time frame compared to most disputes that go before the key D.C. appeals court, but still doesn’t seem to be moving quickly enough to have a direct impact on the ongoing impeachment process against Trump.

U.S. District Court Judge Ketanji Jackson, an Obama appointee, handed down a ruling on Nov. 25 rejecting the Justice Department’s claims of absolute immunity for McGahn.

Two days later, Henderson, Rogers and Griffith issued an administrative stay, freezing further action in the case while the judges considered the Trump administration’s request for a pause on the ruling until the appeal is resolved.

Even if the appeals court rules within a week or so of the Jan. 3 arguments, the case is all but certain to be taken to the Supreme Court and could be delayed in the meantime by a petition to the full bench of the D.C. Circuit.

Meanwhile, the House is expected to vote to impeach Trump sometime this week over articles related to Trump’s pressure campaign on Ukraine. The process will then move to the Senate for an impeachment trial sometime in January. Senate Minority Leader Chuck Schumer has proposed starting the trial on Jan. 7, although Senate Majority Leader Mitch McConnell may not go along with such an ambitious time frame.

Another consideration is that even if McGahn was forced to appear for a deposition or public testimony at a Judiciary Committee hearing, he or White House lawyers would likely have the opportunity to levy claims of executive privilege on a question-by-question basis. Those, too, could end up in court, further dragging out the process.

In the near term, then, the outcome of the McGahn court fight may simply offer one side the chance to publicly crow about a legal win in a high-profile conflict. In the long term, however, the result could set a precedent that would alter the balance of power between presidents and Congress for decades to come.

Other signers on the GOP lawyers’ brief include former Reps. Steve Bartlett of Texas, Jack Buechner and Thomas Coleman of Missouri, Bob Inglis of South Carolina, Jim Kolbe of Arizona, Steven Kuykendall of California, Mike Parker of Mississippi, Thomas Petri of Wisconsin, Peter Smith of Vermont and Dick Zimmer of New Jersey.

The brief also has the support of ex-Federal Election Commission Chairman Trevor Potter, former Justice Department official Jonathan Rose, former Homeland Security official Paul Rosenzweig and George Mason law professor J.W. Verret.