The U.S. Supreme Court is set to hear what could become the biggest cases involving Donald Trump as president, a pair of constitutional clashes that could insulate chief executives from investigations while in office and add an explosive new element to the 2020 election campaign.

Trump is trying to keep House Democrats and a New York prosecutor from seeing his financial records. The high court will hear back-to-back arguments Tuesday — by phone and livestreamed because of the coronavirus outbreak — on Trump's efforts to block his banks and accountants from complying with subpoenas they have received.

The court's rulings could determine whether the president's tax returns become public, and whether he faces an accelerated criminal investigation in New York. It will pose one of the toughest tests yet for Chief Justice John Roberts' court, forcing it to navigate politically polarizing and constitutionally weighty issues less than six months before the presidential election.

"I do think they will be searching — I hope they will be searching — for a way to resolve the cases that rises above the partisan division that infects so much else in the United States," said David Cole, legal director for the American Civil Liberties Union, which is urging the court to reject Trump's challenges.

The clashes summon memories of cases involving two other heavily investigated presidents, Richard Nixon and Bill Clinton. In 1974 the Supreme Court unanimously forced Nixon to turn over the secret White House tape recordings that led to his resignation. The court was unanimous again in 1997 in ruling that a sexual harassment suit against Clinton could go forward while he was in office.

The subpoenas seek years of Trump's personal financial records, as well as those of the Trump Organization and his other businesses. They are directed to Trump's accounting firm, Mazars USA, and his banks, Deutsche Bank AG and Capital One Financial Corp. The accountants and banks aren't contesting the subpoenas and have said they will comply with their legal obligations.

Though the legal issues are distinct, the two cases share overarching themes. In each, Trump's personal lawyers and his administration's Justice Department say the lower courts that ruled against him were insufficiently sensitive to the intrusive nature of a demand for a sitting president's personal records. In each, Trump's adversaries say the president is effectively trying to put himself above the law.

And in each, Democrats are trying to finally see the tax returns Trump refused to release as a candidate and then as president. Until Trump, every president dating back to Jimmy Carter made his returns public.

The House subpoena case focuses on the power of Congress to demand presidential documents outside of impeachment investigations. Three House committees — Oversight, Financial Services and Intelligence — say they are pursuing legislative goals, including updating ethics laws and trying to guard against foreign influence in the 2020 election.

House lawyers said the Supreme Court "has long recognized that Congress may investigate potential wrongdoing if the investigation relates to a valid legislative purpose."

But Trump's team says the committees' real pursuit isn't legislation but law enforcement, a goal the president's team says is beyond Congress' constitutional authority.

"The events that led to the subpoenas' issuance, the public statements surrounding these investigations, the nature of these demands themselves, and other evidence confirm that the committees' purpose is to find out if the president broke the law," Trump's private lawyers argued.

In the grand jury case, Trump contends the president has complete immunity from criminal investigations while in office. He says that any investigation, even one in which the document demand goes to a third party, risks being a distraction from the chief executive's responsibilities.

"The president cannot effectively discharge those duties if any and every prosecutor in this country may target him with criminal process," Trump's lawyers argued.

Manhattan District Attorney Cyrus Vance Jr. is investigating whether the Trump Organization falsified business records to disguise hush payments to two women who claimed they had sex with Trump before he took office.

Vance and his supporters say presidents throughout history, including Nixon and Clinton, have been subject to judicial proceedings. Vance says a complete shield from investigation is especially inappropriate in a probe that doesn't touch on the president's official duties.

"Immunity from investigation for private conduct runs counter to precedent, the structure and operation of the Constitution, and the bedrock principle that no person is above the law," Vance argued.