The Trump administration and the House will square off in court on Tuesday over former White House counsel Don McGahn’s refusal to comply with a congressional subpoena for his testimony as part of the impeachment inquiry.

While that investigation has been dormant for months and eclipsed by the coronavirus health crisis, the case could have serious ramifications for Congress's ability to investigate the executive branch.

“What's at stake is the very capacity of Congress to exercise its investigative power with regard to the president,” said Peter Shane, a constitutional law professor at Ohio State University. 

The D.C. Circuit is rehearing the case after a panel of three judges ruled 2-1 earlier this year that Congress did not have standing to have its subpoenas enforced by the courts. The majority said the Constitution prevents courts from mediating disputes between the political branches of government.

“If we order McGahn to testify, what happens next? McGahn, compelled to appear, asserts executive privilege in response to the Committee’s questions,” Judge Thomas Griffith, who was appointed to the court by George W. Bush, wrote in the opinion. “The Committee finds those assertions baseless. In that case, the Committee assures us, it would come right back to court to make McGahn talk."

“The walk from the Capitol to our courthouse is a short one, and if we resolve this case today, we can expect Congress’s lawyers to make the trip often,” Griffith added.

If that ruling had stood, lawyers for the House said it would have rendered congressional investigative demands legally unenforceable.

“The panel’s contrary decision upends separation-of-powers principles,” the House’s lawyers said in a brief earlier this month. “Judicial resolution of subpoena disputes safeguards the separation of powers by ensuring that Congress can obtain information needed to perform its constitutional functions and serve as an effective check on the Executive.”

Both sides now will be presenting their arguments before a larger panel of nine judges. Due to the COVID-19 crisis, the oral argument hearing will be conducted by phone conference.

Trump last year directed McGahn not to comply with a subpoena from the House Judiciary Committee, asserting that he and his advisers have “absolute immunity” to congressional subpoenas, prompting the House committee to file a lawsuit seeking to have its demand enforced by a judge.

A district court judge sided with the Democrats, rejecting Trump’s broad assertions of immunity as “baseless” and ordering McGahn to comply with the subpoena. The DOJ appealed and won the favorable panel ruling from Griffith, which was then vacated in order for the circuit court to rehear the case.

The case is one of many fronts in Trump’s battle against congressional oversight, which has spawned an unprecedented number of court cases between the administration and the legislative branch. Next month, the Supreme Court will hear oral arguments in a case that will decide whether congressional subpoenas for the president’s personal financial records are valid.

The administration has repeatedly refused to comply with congressional requests for information and subpoenas, and has argued in court that the House cannot sue to force compliance.

“For the first two centuries of this Nation’s history, the political branches of the federal government resolved disputes between themselves through political contest and compromise, not by asking the judicial branch to pick a side in zero-sum litigation,” the Justice Department wrote in a brief in March. “That tradition reflects our Constitution’s fundamental separation-of-powers principles, which allow federal courts to adjudicate concrete disputes concerning the rights of individuals but bar them from refereeing institutional grievances over the political branches’ respective prerogatives.”

Congress, the DOJ argues, has plenty of legislative powers to use as leverage for its investigative subpoenas, ranging from appropriations to impeachment — a position that was echoed in Griffith’s panel decision earlier this year. 

The House has argued that such methods are not practical for routine subpoenas and information requests.

“The panel suggested that Congress could use political tools — such as contempt and even impeachment — to force compliance, but the constitutional brinksmanship envisioned by the panel would heighten interbranch conflict and undermine, not protect, the separation of powers,” the House wrote in its brief earlier this month. “In any event, recent experience confirms that political tools cannot force an obstinate Executive to cooperate with legitimate Congressional inquiries.”

Trump has also incorporated his administration’s stance against congressional oversight into the $2 trillion relief package passed by Congress last month. The president issued a signing statement saying he believed requirements in the bill that the inspector general for the program report to Congress are unconstitutional, reflecting the stance his administration had taken in its numerous court battles with House Democrats.

If the House ends up losing the McGahn case, it may have little authority to exercise effective oversight of the administration’s handling of the massive coronavirus bailout, or any other executive branch operations for that matter.

Some legal scholars contend that Trump’s stance toward oversight represents a sharp departure from those of recent administrations.

“The idea that someone could simply ignore a House subpoena, or a Senate subpoena for that matter, because they had worked for the president is just at odds with what heretofore has been everyone's understanding of the scope of the subpoena power,” Shane, the Ohio State professor, told The Hill.

“Without routine compliance of congressional subpoenas, the power of Congress to investigate the executive branch effectively is eviscerated,” he added.