The US Supreme Court has made it clear that a sitting president cannot evade criminal investigations, ruling that a prosecutor in New York City can obtain President Donald Trump's financial records including tax returns.

The 7-2 ruling authored by Chief Justice John Roberts means that the subpoena issued to Mr Trump's long-term accounting firm, Mazars LLP, for various financial records to be turned over to a grand jury as part of a criminal investigation can be enforced.

"Two hundred years ago, a great jurist of our Court established that no citizen, not even the President, is categorically above the common duty to produce evidence when called upon in a criminal proceeding," the court said.

"We reaffirm that principle today."

However, the court has thrown out rulings allowing Democratic-led congressional committees to obtain Mr Trump's financial records. It sent the dispute back to lower courts.

In response, Mr Trump said he was the victim of "political prosecution".

"This is all a political prosecution," he tweeted.

"I won the Mueller Witch Hunt, and others, and now I have to keep fighting in a politically corrupt New York. Not fair to this Presidency or Administration!"

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Unlike other recent presidents, Mr Trump has refused to release his tax returns and other documents that could provide details on his wealth and the activities of his family real estate company, the Trump Organization.

The content of these records has remained a persistent mystery even as he seeks re-election on 3 November.

House committees issued subpoenas seeking Mr Trump's financial records from his longtime accounting firm Mazars LLP and two banks, Deutsche Bank and Capital One.

As part of a criminal investigation by the office of Manhattan District Attorney Cyrus Vance, a Democrat, subpoenas were issued to Mazars for financial records, including nearly a decade of Mr Trump's tax returns to be turned over to a grand jury in New York City.

The investigation launched by Mr Vance's office in 2018 into Mr Trump and the Trump Organization was spurred by disclosures of hush payments to two women who said they had past sexual relationships with him, adult film actress Stormy Daniels and former Playboy model Karen McDougal.

Mr Trump and his aides have denied the relationships.

In the litigation over the House subpoenas, Mr Trump argued that Congress lacked a valid purpose for seeking his records and that disclosure of the material would compromise his and his family's privacy and distract him from his duties.

In the New York case, Mr Trump's lawyers argued that under the Constitution he is immune from any criminal proceeding while serving as president.

They also cited Justice Department guidance that a sitting president cannot be indicted or prosecuted.

Taxing times for Donald Trump

In a lower court hearing, Mr Trump's lawyers went so far as to argue that law enforcement officials would not have the power to investigate Mr Trump even if he shot someone on New York's Fifth Avenue.

The House Oversight Committee in April 2019 issued a subpoena to Mazars seeking eight years of accounting and other financial information in response to the congressional testimony of Michael Cohen, Mr Trump's former lawyer.

Mr Cohen said Mr Trump had inflated and deflated certain assets on financial statements between 2011 and 2013 in part to reduce his real estate taxes.

The House Financial Services Committee has been examining possible money laundering in US property deals involving Mr Trump.

In a separate investigation, the House Intelligence Committee is investigating whether Mr Trump's dealings left him vulnerable to the influence of foreign individuals or governments.

Mr Vance called the ruling "a tremendous victory for our nation's system of justice and its founding principle that no one, not even a president, is above the law".

"Our investigation, which was delayed for almost a year by this lawsuit, will resume, guided as always by the grand jury's solemn obligation to follow the law and the facts, wherever they may lead."

Even if Mr Trump's financial records are turned over to prosecutors they may remain hidden from public view because of grand jury secrecy.

Nancy Pelosi, Democratic speaker of the House of Representatives, said she would continue to press for Mr Trump's financial records to be handed over to Congress.

"The Congress will continue to conduct oversight For The People, upholding the separation of powers that is the genius of our Constitution," Ms Pelosi said.

"We will continue to press our case in the lower courts."