On Monday, D.C. District Court Judge Ketanji Brown Jackson issued a 120-page opinion ordering former White House counsel Don McGahn to comply with a subpoena to appear before a House committee as it considers impeachment of President Donald Trump.

“Don McGahn will comply with Judge Jackson’s decision unless it is stayed pending appeal,” said McGahn’s attorney, William Burck, after the ruling came down.

The Department of Justice, which asserted absolute immunity for McGahn on the president’s behalf, promised to appeal the case. If the ruling is upheld at the D.C. Circuit level and the Supreme Court, it would have profound consequences for the House impeachment inquiry.

McGahn’s testimony would likely focus on Trump’s efforts to obstruct the Mueller investigation as described by the Mueller report. But there is potentially an even greater import here. McGahn left the White House well before the Ukraine bribery scandal at the center of the current impeachment inquiry began to unfold, but the ruling was written in such a way that if upheld it would extend to current and former White House aides at the center of that scandal, such as former national security adviser John Bolton and acting White House chief of staff Mick Mulvaney. CBS News reported that “a source familiar with Mulvaney’s legal strategy [said], he will not comply with any of these decisions.” If the Supreme Court ultimately upholds this decision, though, and the House Intelligence Committee subpoenas Mulvaney, it’s unclear what choice he’ll have.

Mulvaney, who has stated publicly that the Trump administration withheld hundreds of millions of dollars in military aid to pressure Ukraine to investigate the Democratic National Committee, must now hope that the impeachment inquiry and trial are complete before the D.C. Circuit Court and the Supreme Court take up an appeal of Jackson’s ruling. The circuit level will have every incentive to fast-track the case, so we may get news on this fairly soon.

Jackson was clear on what the law here holds. “Stated simply, the primary takeaway from the past 250 years of recorded American history is that Presidents are not kings,” Jackson wrote, citing James Madison, Alexander Hamilton, and Alexis de Tocqueville. Trump’s broad claim of absolute immunity from testimony by close aides would “distort established separation-of-powers principles beyond all recognition.”

Jackson relied heavily on the 2008 case Committee on the Judiciary, U.S. House of Representatives v. Harriet Miers, in which another D.C. District Court judge ruled that the Judiciary Committee “had the power to compel former White House Counsel Harriet Miers and then-White House Chief of Staff Joshua Bolten to testify and produce documents in connection with a congressional investigation.” That case ultimately ended once George W. Bush was out of office, so Miers was never forced to testify. That means there was no appellate decision to bind Jackson in the McGahn case. However, Jackson found the legal arguments of the Miers decision to be persuasive.

While the ruling itself is fairly narrow—holding only that the White House cannot cite absolute immunity to prevent McGahn from testifying and not ruling on individual instances of executive privilege he might cite during testimony—it was written in a way to extend well beyond McGahn’s testimony alone.

“This Court reiterates Miers’s well-sourced and thoroughly explained bottom-line conclusion: that, as a matter of law, senior-level current and former presidential aides, including White House Counsels, must appear before Congress if compelled by legislative process to do so,” she wrote. “This means that such aides cannot defy a congressional subpoena on the basis of absolute testimonial immunity, even if the President for whom they work (or worked) demands that response.”

Bolton’s and Mulvaney’s testimony is critical to the Ukraine matter, particularly as House Republicans spent the past two weeks rejecting the inquiry’s current witnesses as not having had firsthand interactions with the president. In the first round of impeachment depositions and hearings, one of the top advisers working under Bolton at the National Security Council, Fiona Hill, testified that Bolton viewed the Ukraine pressure campaign as a “drug deal” being cooked up by Mulvaney and Ambassador to the European Union Gordon Sondland.

Bolton and his attorney are currently embroiled in a separate case to determine whether he would have to comply with a congressional subpoena. (A subpoena has not yet been issued for Bolton’s testimony. It’s unclear whether one is forthcoming, but House Intelligence Committee chairman has rightly insisted that Bolton should testify.) That case now seems moot. Indeed, Jackson preemptively addressed one of the key legal arguments made by Bolton’s attorney in that separate case. Charles Cooper, who represents both Bolton and his deputy Charles Kupperman, argued that a ruling separate from the McGahn matter was necessary in Kupperman’s and Bolton’s cases because “information concerning national security and foreign affairs” would be at the center of their testimony. Jackson made a point to note that McGahn’s work also touched on national security and that was not an impediment to him complying with a subpoena.

For good measure, Jackson reiterated later in the decision that, as far as subpoena compliance is concerned, it does not “make any difference whether the aides in question are privy to national security matters, or work solely on domestic issues.” The judge in the Kupperman-Bolton case must decide whether to move forward now that Jackson has issued her ruling, particularly given the fact that the House Judiciary Committee has dropped its subpoena of Kupperman and not yet even issued one of Bolton.

Perhaps most satisfyingly, Jackson’s ruling is unsparing in its analysis that DOJ’s legal position seeks to place the president above the law. Absolute immunity, she wrote, “has no foundation in law” and “conflicts with key tenets of our constitutional order.”

Jackson continued:

If there is fraud or abuse or waste or corruption in the federal government, it is the constitutional duty of Congress to find the facts and, as necessary, take corrective action. Conducting investigations is the means that Congress uses to carry out that constitutional obligation. Thus, blatant defiance of Congress’ centuries-old power to compel the performance of witnesses is not an abstract injury, nor is it a mere banal insult to our democracy. It is an affront to the mechanism for curbing abuses of power that the Framers carefully crafted for our protection, and, thereby, recalcitrant witnesses actually undermine the broader interests of the People of the United States.

Ultimately, Jackson could not “abide DOJ’s less-than-subtle suggestion that, under our constitutional scheme, the Legislature and the Judiciary are both hopelessly stymied when it comes to addressing alleged abuses by the Executive branch, such that, ultimately, the President wields virtually unchecked power.” We now have to hope that the Supreme Court cannot abide it either.