WASHINGTON (NYTIMES) - It was a month before Donald Trump's inauguration, and one of his aides had a delicate question: Wasn't there going to be a backlash when it became known that the inauguration had spent donors' money at Mr Trump's hotel in Washington, even though other places would cost much less or even be free?

"These are events in P.E.'s honour at his hotel, and one of them is with and for family and close friends," Stephanie Winston Wolkoff, then an event planner for Mr Trump, wrote in an e-mail to a colleague in December 2016, referring to Trump as the president-elect and saying she raised the issue to "express my concern".

As Mr Trump's presidency comes to a close, expenditures like those are receiving renewed legal scrutiny in the form of a civil case being pursued by the attorney general for the District of Columbia.

At the heart of the case is a question - whether Mr Trump and his family have profited from his public role, sometimes at the expense of taxpayers, competitors and donors - that has been a persistent theme of his tenure in the White House.

More than 200 companies, special-interest groups and foreign governments patronised Mr Trump's properties during his presidency while reaping benefits from him and his administration. Sixty of them spent US$12 million (S$16 million) at his properties during the first two years he was in office.

The Trump family business has received millions of dollars in payments by the Secret Service, the State Department and the US military to Trump properties around the country and the world.

The president has visited his properties on at least 417 days since taking office, at times with world leaders. And he and his affiliated political committees spent more than US$6.5 million in campaign funds at his hotels and other businesses since 2017, including a US$1 million final burst in the weeks before the election last month.

In the lawsuit moving forward, Attorney General Karl A. Racine of Washington is arguing that Mr Trump's inaugural committee illegally overpaid his family business by as much as US$1.1 million for events held at the Trump International Hotel in the city in January 2017.

Ms Ivanka Trump was deposed in the case last week.

Questions about spending, influence and lobbying around the 2017 inaugural have also drawn scrutiny from federal prosecutors from two different offices in New York, with charges filed against at least one donor.

But for all the attention focused on the issue, Mr Trump is set to leave office without a clear resolution of what limits there should be on a president's ability to profit from his public role.

Lawsuits brought by nonprofit groups and attorneys general in Washington and Maryland claiming that Mr Trump had violated the so-called emoluments clause of the Constitution were never resolved during his term and now face potential dismissal once he is out of power.

"It is more than just frustrating," said Laurence H. Tribe, a constitutional law professor at Harvard University, who has been involved in the emoluments litigation. "The most serious questions about the abuse of presidential power and the use of the presidency as a centre of personal gain and profit remain unresolved. The wheels of justice clearly ground more slowly than some would have hoped."

The issue played out especially visibly at the Trump International Hotel in Washington, which opened in late October 2016, two weeks before Mr Trump was elected.

The hotel became a focal point for lobbyists, White House aides, Republicans in Congress and hundreds of others who sought a way to impress Mr Trump, even though tax records obtained by The New York Times show that the property continued to lose money through at least 2018.

The case Mr Racine is pursuing is moving ahead after he spent several years collecting evidence about the arrangements between the presidential inaugural committee and the hotel.

Mr Trump's inauguration was unlike any other in U.S. history: He raised more than US$107 million, twice the previous record, as corporate donors poured tens of millions of dollars into the inaugural committee. Spending also took place at a record rate.

At the Trump hotel, the inaugural committee and guests attending the inauguration were already planning to fill most of the 263 rooms, which Mr Racine argued meant that ballroom space would typically be offered for free or at least at a major discount.

But when the hotel initially asked the inaugural committee to pay US$450,000 a day to rent the ballrooms and other common spaces, it provoked immediate questions from both Wolkoff, who has since broken with the Trump family, and Rick Gates, then the inaugural committee's deputy chair, who would go on to plead guilty to charges stemming from the special counsel's investigation.

"First, the cost itself seems quite high compared to other property buyouts for the week," Mr Gates wrote in an e-mail to Ivanka Trump 38 days before the inauguration.

"Second, I am a bit worried about the optics of PIC paying Trump Hotel a high rent fee and the media making a big story out of it," he added, referring to the presidential inaugural committee.

Mr Trump wrote to Mickael C. Damelincourt, the hotel's general manager, and asked him to call Gates to negotiate a better deal for the inaugural committee. "It should be a fair market rate," she said in a follow-up email, which soon led to a new offer of US$175,000 per day.

Ms Ivanka Trump was questioned for five hours last week about the matter, in one of a series of depositions that has also included Damelincourt and Thomas J. Barrack Jr., a major donor to Donald Trump who was the chair of the inaugural committee. Wolkoff will be questioned under oath this week and Gates this month.

Documents were also subpoenaed from Mrs Melania Trump, the first lady, but she has not been called to testify.

After her deposition, Ms Ivanka Trump condemned the inquiry, as did her brother Eric Trump, who oversees operations at the hotel.

"This is a game stemming from a political vendetta," Mr Trump said in an interview, echoing his sister, who said on Twitter that the case was "another politically motivated demonstration of vindictiveness & waste of taxpayer dollars."

So far, Judge José M. López at the Superior Court of the District of Columbia has sided with the attorney general, rejecting a motion by the Trump Organisation and the inaugural committee to dismiss the case. Mr López has authorised the parties to move ahead with depositions and other discovery until March to prepare for a possible trial.

The civil suit pursued by Mr Racine is distinct from two separate cases raising the constitutional issues about the intersection of Donald Trump's public role and his businesses. The two cases focused on the Constitution's emoluments clause will be on shakier ground once he leaves office, lawyers involved in the cases said.

A US District Court judge ruled in one of the emoluments suits in March 2018 that Maryland and the District of Columbia had the right to pursue their cases challenging whether Mr Trump's businesses could take payments from other governments. And for the first time, the court defined what an emolument is, accepting the broader definition advocated by Maryland and the District of Columbia that it represented just about any payment from a foreign government to the president's businesses instead of a payment made to the president explicitly in exchange for an official action he would then take, as he had argued.

But one of the remedies their lawsuit sought was an order that the president stop accepting these payments. Once he leaves office, that outcome will effectively have been achieved, perhaps undermining the case.

"We are having high-level discussions around the viability, survivability of the matter," Mr Racine said about the emoluments case.