President Trump asked the Supreme Court on Thursday to stop a prosecutor’s investigation of his personal finances, a bold assertion of presidential power that seeks a landmark decision from the nation’s highest court.

The filing by the president’s private lawyers represents a historic moment that will test the court and highlights the Constitution’s separation-of-powers design. It also marks a new phase in the investigations that have dogged Trump throughout his presidency and have culminated in an impeachment inquiry.

The case involves Manhattan District Attorney Cyrus Vance Jr.’s attempt to enforce a grand jury subpoena issued to the president’s accountants for eight years of Trump’s tax records.

Trump went to court to block the subpoena, making a broad claim that U.S. presidents are immune from investigation while in office. A district judge and a panel of the U.S. Court of Appeals for the 2nd Circuit ruled against him, saying that the subpoena was proper and that the president’s longtime accounting firm, Mazars USA, must comply.

Vance’s office, which declined to comment Thursday, agreed to hold off on enforcing the subpoena if Trump’s lawyers quickly asked the Supreme Court to hear the case this term.

“For the first time in our nation’s history, a state or local prosecutor has launched a criminal investigation of the President of the United States and subjected him to coercive criminal process,” wrote Jay Sekulow, one of the president’s lawyers.

Since 2016, President Trump has cited an ongoing IRS audit as the primary reason that he will not release his tax returns. (Monica Akhtar/The Washington Post)

He added: “Politically motivated subpoenas like this one are a perfect illustration of why a sitting president should be categorically immune from state criminal process.”

The justices are not required to review the lower court’s decision. But the chances that the high court will get involved increased Wednesday when a separate appeals court in a separate case concluded that Congress has a right to the same tax records. Trump’s lawyers plan to ask the Supreme Court on Friday for a stay in that case.

The cases set up a potentially dramatic decision on presidential power like those the Supreme Court rendered against Presidents Richard M. Nixon and Bill Clinton. Both were unanimous rulings rejecting their pleas, and they suggest Trump might have trouble shielding the tax information from prosecutors and Congress.

The case will come before a court that includes two Trump nominees, Justices Neil M. Gorsuch and Brett M. Kavanaugh. In addition, Justice Ruth Bader Ginsburg in media interviews before the 2016 election criticized Trump’s decision not to release his tax information, as other presidential nominees had done.

“How has he gotten away with not turning over his tax returns?” Ginsburg said in an interview with CNN. “The press seems to be very gentle with him on that.” After criticism, Ginsburg said she should not have commented on the candidate.

The Supreme Court’s decision on whether to review the issue will be made in the coming weeks. If a review is granted, there probably would be time for a full hearing before the justices this term and a ruling in the coming presidential election year.

Trump has moved aggressively to block examination of his tax records, filing lawsuits against congressional committees, two banks and Mazars, which has said it will turn over the records if courts so order.

Other separation-of-powers cases that could reach the Supreme Court include Congress’s effort to access redacted portions of special counsel Robert S. Mueller III’s report on Trump’s 2016 campaign and Russian interference in that year’s election, and lawsuits alleging that Trump’s private businesses violate the emoluments clauses of the Constitution.

Vance has said his office needs the records for its investigation into alleged hush-money payments during the 2016 campaign to Stormy Daniels, an adult film actress, and to former Playboy model Karen McDougal. Both women said they had affairs with Trump, and Vance’s office is examining whether any Trump Organization officials filed falsified business records, in violation of state law, related to the payments. Trump has denied the affairs and any wrongdoing.

Trump attorney William S. Consovoy has argued that while in the White House, Trump has “temporary presidential immunity” not just from prosecution, but also from investigation. At the appeals court hearing in New York, Consovoy said in response to a judge’s question that the president, for as long as he is in office, could not be investigated even for shooting someone on the streets of Manhattan.

The Justice Department filed a brief in support of the president, but it did not endorse Trump’s assertion that he has absolute immunity from investigation. Instead, government lawyers said that there are instances when a local prosecutor might legally seek a president’s documents — but that this was not one of them.

Vance has rejected Trump’s sweeping immunity claims, saying the president is seeking to “invent and enforce a new presidential ‘tax return privilege’ ” that would bar anyone from seeing his returns. “No such privilege exists in the law,” Vance’s office said in court filings at the 2nd Circuit.

U.S. District Judge Victor Marrero in New York called Trump’s theory “repugnant to the nation’s governmental structure and constitutional values.”

A unanimous panel of the 2nd Circuit issued a more-subdued ruling against Trump.

Chief Judge Robert A. Katzmann, writing for the majority, noted the Supreme Court’s 1974 decision ordering the White House to turn over Nixon’s audiotapes during a criminal investigation of his aides.

Trump “has not persuasively explained why, if executive privilege did not preclude enforcement of the subpoena issued in Nixon, the Mazars subpoena must be enjoined despite seeking no privileged information and bearing no relation to the president’s performance of his official functions.”

Katzmann’s decision was far more limited, he said, and did not address whether Trump was subject to prosecution.

“The only question before us is whether a state may lawfully demand production by a third party of the president’s personal financial records for use in a grand jury investigation while the president is in office,” Katzmann wrote.

He added in a footnote:

“We note that the past six presidents, dating back to President Carter, all voluntarily released their tax returns to the public. While we do not place dispositive weight on this fact, it reinforces our conclusion that the disclosure of personal financial information, standing alone, is unlikely to impair the president in performing the duties of his office.”

In the filing at the Supreme Court, Trump’s lawyers said that upholding the subpoena would unleash the president’s political enemies.

“That the Constitution would empower thousands of state and local prosecutors to embroil the President in criminal proceedings is unimaginable,” they said in the filing. “State criminal process interferes with the President’s ability to execute his duties.”

But Vance has noted that, unlike disputes involving past presidents, the New York subpoena does not require any action from Trump because it is aimed at his accounting firm.

Trump’s separate suit against the House Oversight and Reform Committee became ripe for Supreme Court review Wednesday when the full U.S. Court of Appeals for the D.C. Circuit declined to review a ruling against Trump by a panel of the court.

A divided three-judge panel of that court held in October that the House had issued its subpoena for “legitimate legislative pursuits, not an impermissible law-enforcement purpose,” as the president’s lawyers had argued.

“Contrary to the president’s arguments, the committee possesses authority under both the House rules and the Constitution to issue the subpoena, and Mazars must comply,” wrote Judge David S. Tatel, who was joined by Judge Patricia A. Millett. Both were nominated by Democratic presidents.

Judge Neomi Rao, a Trump nominee, had dissented in the case, and she was joined by two other Republican-nominated judges in unsuccessfully advocating for a rehearing.

Judge Gregory Katsas, a Trump nominee who had earlier worked in the White House Counsel’s Office, called the congressional subpoena a “threat to the presidency” and warned that it would be “open season on the president’s personal records” if Congress is allowed to compel the president to disclose personal records on the basis of the possibility that it might inform legislation.