People stop to read messages written by protesters posted on a wall outside the official opening of the Trump International Hotel and Tower in Vancouver late last month. (Darryl Dyck/Associated Press)

A trio of watchdog groups has asked the U.S. attorney for the Southern District of New York to investigate whether President Trump has received payments or other benefits from foreign governments through his business interests in violation of an obscure clause in the U.S. Constitution.

The request, sent by letter Wednesday morning to U.S. Attorney Preet Bharara, is a novel strategy by ethics critics who have been pressing Trump to comply with the Constitution’s “emoluments clause,” which prohibits top officials from receiving payments or favors from foreign governments. Trump’s business empire stretches across the globe. The letter was sent six weeks after one of the groups filed a lawsuit in federal district court making a similar claim.

Trump has said he addressed ethics concerns by turning over management of his business to his adult sons, who’ve said they have separated the family business from their relationship with their father and the U.S. government.

“There are lines we would never cross,” Eric Trump told The Washington Post in a recent interview, “and that’s mixing business with anything government.”

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(Jenny Starrs/The Washington Post)

On Wednesday, the White House referred questions to the Trump Organization, where attorney Alan Garten dismissed the letter as “factually inaccurate, legally erroneous and politically motivated.”

Although the president has relinquished day-to-day management of his businesses, his critics say his continued ownership interest means he effectively receives benefits from foreign entities, in violation of the Constitution. The ethics advocates, mostly Democrats, have held news conferences and filed a lawsuit. Now they are asking one of the country’s leading federal prosecutors for help.

“We call on you as the United States Attorney for the jurisdiction where The Trump Organization is located to exercise your responsibility to investigate and take appropriate action to ensure that the Trump Organization and related Trump business enterprises do not receive payments and financial benefits from foreign governments that benefit President Trump,” the letter said. It is signed by Fred Wertheimer, president of Democracy 21, bipartisan leaders of the Citizens for Responsibility and Ethics in Washington organization (CREW), and Paul Smith of the Campaign Legal Center.

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“It cannot be the case that the president can flagrantly violate the Constitution and get away with it,” said Norman L. Eisen, who served as ethics counsel under President Barack Obama. Eisen, who signed the letter as chairman of CREW, acknowledged that asking a U.S. attorney to investigate a matter involving a sitting president is unusual. But, he said, “having a president with these conflicts is also unprecedented.” The letter is also signed by CREW’s vice chair, Richard Painter, who served as ethics counsel to President George W. Bush.

In January, CREW filed suit against Trump in federal district court arguing that his continued receipt of payments from foreign entities violated the Constitution’s emoluments clause. Trump’s reply in that case is due April 1. Eisen said the request to the U.S. attorney should not be seen as a sign that the suit will not move forward. “We believe our complaint in the judicial branch should not exclude review by the other branches of government,” he said, citing the importance of the emoluments restriction.

That clause says that “no Person holding any Office of Profit or Trust under [the United States], shall, without the Consent of the Congress, accept of any present, Emolument, Office, or Title, of any kind whatever, from any King, Prince, or foreign State.” It was written in to Article I out of concern that the fledgling country’s leaders could be influenced by a wealthy European power.

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The meaning of the clause has not been rigorously tested. The watchdog groups say the text should be interpreted to mean that Trump’s businesses should cease commercial transactions with foreign states.

The letter notes that China recently granted Trump a trademark for building construction services. It also points out that tenants of Trump Tower in New York include a Chinese bank and the Abu Dhabi Tourism and Culture Authority, and that the Trump hotel in Washington has been courting business from foreign diplomats. The document notes that Trump’s business entities have plans to build luxury hotels in China, and that it is also engaged in real estate and licensing projects in India, Indonesia, the Philippines, Saudi Arabia, Scotland, Taiwan and Turkey.

“We believe the Justice Department has a broad mandate to ensure compliance with provisions of the Constitution that relate to Federal officeholders,” the letter said.

The letter noted testimony of Attorney General Jeff Sessions in his confirmation hearings. Sessions stated that although he was not aware of a federal law that directly charges the Justice Department with enforcing the emoluments clause, he recognized that the Justice Department has the responsibility “to ensure that officeholders comply with their constitutional obligations.”

Wertheimer said that the request was made because he sees “a powerful record that President Trump is receiving benefits that do not comply with the emoluments clause.” He and other signers said Bharara was chosen in part because he is known for fierce independence. Since he was appointed in 2009 he has investigated New York Gov. Andrew M. Cuomo and New York City Mayor Bill De Blasio, both Democrats. Although Bharara was appointed by Obama, Trump met with him after the election and asked him to stay on as U.S. attorney.