An empty chair for former White House counsel Donald McGahn prior to a House Judiciary Committee hearing on Capitol Hill in Washington on May 21. (Shawn Thew/EPA-EFE/Shutterstock)

ANOTHER WEEK, another empty witness chair as President Trump continues his unprecedented, unjustifiable stonewalling of Congress. This time, the witness who failed to show was former White House counsel Donald McGahn, a key figure in the obstruction-of-justice inquiry that special counsel Robert S. Mueller III recently completed. The White House ordered Mr. McGahn to spurn Congress.

Mr. Trump’s contempt of Congress’s investigative prerogatives is eliciting a reaction. House Speaker Nancy Pelosi (D-Calif.) is struggling to keep Democrats united behind a patient strategy of information-gathering and legislative pressure rather than moving immediately toward impeachment hearings.

That is why Monday’s ruling from U.S. District Judge Amit P. Mehta was important, showing that the dispute can be refereed in an orderly fashion that may satisfy congressional Democrats — and the public’s right to know — without resorting to immediate impeachment proceedings or other more extreme measures that Democrats are considering to compel administration cooperation. Mr. Mehta repudiated the president’s lawyers, who argued that congressional Democrats could not legally compel disclosure of financial records from Mr. Trump’s accounting firm. More importantly, the judge did so quickly, denying the need for additional proceedings and getting to a final decision just days, not weeks or months, after oral arguments.

One understandable reason for Democratic concern is that the president’s stonewalling might allow him to escape public accountability simply by running out the clock. Mr. Trump has essentially told Congress, “I’ll see you in court.” Even if judges eventually vindicate House Democrats — who have the better side of the legal case in many of the disagreements with the administration — Mr. Trump could still win by delaying the reckoning, particularly if nothing is settled before the 2020 presidential election.

If judges seem poised to let Mr. Trump win by delay, their inaction would itself factor into the politics. They would make impeachment more likely and more justifiable. That is why the U.S. Court of Appeals for the District of Columbia Circuit, the appeals court next in line to consider Mr. Mehta’s ruling, should act with urgency. The same is true with the judges who will consider the other disputes between the White House and Congress over the legislature’s investigative demands.

In the past, the executive and the legislature have usually been able to sort out these kinds of disagreements. But the Trump administration has shown a characteristic absence of good faith. The Post revealed Tuesday that a confidential Internal Revenue Service draft memo found, about the administration’s obligation to turn over Mr. Trump’s tax returns, that the law gives Treasury Secretary Steven Mnuchin no discretion in whether to surrender the president’s tax information to congressional investigators. Mr. Mnuchin refused anyway.

Judges cannot behave as though these are usual times or pretend that the procedure they choose will not have direct political consequences. They should make the Trump cases a priority and act with deliberate speed.