The US Supreme Court is seen following oral arguments in Trump v. Mazars and Trump v. Deutsche Bank AG, dealing with the…
The U.S. Supreme Court is seen in Washington, May 12, 2020.

President Donald Trump's years-long refusal to release his tax records came before the U.S. Supreme Court on Tuesday as justices weighed whether Congress and local prosecutors have the authority to investigate a sitting president.

The justices heard oral arguments in two high-profile cases involving subpoenas for Trump's tax and other financial records issued by three House of Representatives committees and New York City's top prosecutor to Trump's accounting firm and banks.

Trump, who has doggedly refused to make his taxes public, sought to block the financial institutions from turning over the documents to the investigators, but federal courts in New York and Washington ruled against him last year, prompting Trump's lawyers to appeal the decisions to the Supreme Court.

Three House panels have been investigating Trump and his businesses for the past year. They say they need the information as part of their work. Manhattan District Attorney Cyrus Vance Jr. wants the records as part of a grand jury investigation of hush money payments Trump's former fixer made to two women during the 2016 election.

President Donald Trump speaks in the Rose Garden of the White House, May 11, 2020.

This is the third time in nearly 50 years that the high court has considered whether a sitting president must comply with a legal request for documents.

In the two previous cases — United States v. Nixon in 1973, and Clinton v. Jones in 1997 — the court unanimously ruled against presidents Richard Nixon and Bill Clinton, respectively.

But the high court has taken an ideological turn to the right after Trump appointed conservatives to the bench, raising the likelihood of a split decision, seen in a string of victories the court has handed the president.

"My takeaway is that a majority of the justices were troubled by the breadth of the subpoena issued by Congress," said Saikrishna Prakash, a professor of law at the University of Virginia.

The justices offered few clues about how they will come down, reflecting the need to balance competing interests between the various branches of governments.

The justices' questions, however, sparked speculation among some court watchers that instead of ruling for or against Trump, the court will tighten presidential subpoena standards and send one or both cases back to the lower courts to decide.

The over three-hours-long argument in the penultimate case of the court's current term was conducted by teleconference and livestreamed, as justices and lawyers who were sheltering at home during the coronavirus pandemic phoned in.

A decision in the cases is expected in the coming weeks just as Trump and the presumptive Democratic nominee, former Vice President Joe Biden, gear up for the party conventions ahead of the November presidential election.

The court's decision carries significant implications for separation of powers. In a polarized political environment, depending on the outcome, it could either strengthen the institution of the presidency or the Congress. 

"If they rule in the president's favor, in either case, it'll make it harder for people to investigate the president," Prakash said.

While similar in scope, the two cases touched on different constitutional questions.

Separation of powers

The first case, involving House subpoenas issued to global accounting firm Mazars USA, Capital One and Germany's Deutsche Bank, revolves around the question of separation of powers and congressional power to investigate a president.

Contending that the House subpoenas served no substantial "legislative purpose," Trump lawyer Patrick Strawbridge said that congressional investigators should not be given a "blank check" to investigate the president.

FILE - Justice Neil Gorsuch speaks during an interview in his chambers at the Supreme Court in Washington, Sept. 4, 2019.

Neil Gorsuch, a Trump appointee, asked Trump's lawyer why the House subpoena is not backed by a legitimate legislative purpose.

Strawbridge responded in part by arguing that the House has not explained how the requested documents dating back more than a decade have "anything to do with some purpose that would actually be permissible legislation." 

Douglas Letter, the chief House counsel, said there is a long history of American presidents going back to George Washington responding to congressional requests for information. He argued that Congress could seek information from the president related to any legislation but struggled when asked about limits on subpoena powers.

Presidential immunity

The second case — a subpoena for Trump's taxes and business records issued by a New York grand jury — concerns presidential immunity from prosecution and whether local prosecutors can investigate a sitting president.

Jay Sekulow, another Trump lawyer, argued that the president enjoys "temporary constitutional immunity" from prosecution while in office and that the New York district attorney has no authority to subpoena Trump.

If the subpoena is allowed to stand, he said, it would allow any of the 2,300 district attorneys around the country to "harass, distract and interfere with the sitting president."

Carey Dunne, the general counsel for the Manhattan district attorney, countered that presidents, while immune from criminal prosecution, are not excused from responding to a subpoena. In addition, Dunne said, the information his office is seeking predates Trump's presidential term and is not protected by executive privilege.

There "is a risk that American presidents and third parties unwittingly could end up above the law," Dunne said.