NEW YORK (AFP) - A year ago Donald Trump ceded control of The Trump Organisation to his adult sons, but refused to divest his assets, sparking a furious backlash from political opponents and ethics experts.

Today his golf clubs in Florida and New Jersey, where he spent more than 80 days in 2017, provide a backdrop to his presidency. His opponents complain bitterly and lawsuits have mounted up against opaque ties between the White House and the company.

A prime example of this contentious cocktail of business and politics is the Trump International Hotel in Washington, a six-minute drive from the White House.

If some doubted whether transforming Washington's old post office into a luxury Trump hotel would spell success, today its rooms, restaurants and conference rooms swarm with foreign diplomats and lobbyists.

"The hotel is kind of a separate White House where you can buy a US$27 (S$36) Margarita and where you can talk to people who will talk the next day to the president," says Austin Envers, executive director of American Oversight, a non-profit bankrolled by Democratic donors to expose ethical violations of the Trump administration.

"It's a way to get access to people who work in the administration that regular Americans don't have."

Stays by Saudi and Malaysian delegations were questionable, says Envers, so too an event held by a group representing e-cigarette makers.

A little while later, the administration froze a regulation requiring stricter oversight of the sector.

Trump's habit of making surprise visits to his properties, which has continued in office, has handed them only greater publicity and captivated guests.

"Exceptional service," wrote one recent guest from Australia who gave his name only as David in an online review at Booking.com.

"The extra bonus was when POTUS and FLOTUS showed up standing a couple of feet in front of my wife and me."

POTUS BONUS

But neither is the presidency necessarily an automatic meal ticket either.

The Trump Organisation refused to comment to AFP, but in a recent interview with The New York Times, Eric Trump said the company had decided to focus on existing properties, which include 16 golf courses, a winery, seven hotels and commercial real estate.

As part of the deal made public before the inauguration, the company vowed not to seek new foreign deals while Trump was in office.

In New York, the group has also cut ties with Trump SoHo, which had been boycotted by celebrities and now operates as The Dominick Hotel.

According to US media, several properties in Democratic majority cities such as Chicago and New York have suffered declining interest.

Prior to the 2016 election, the company said it was launching a slightly more affordable hotel chain Scion, a name notable for its lack of obvious connection to Trump. The first is due to open in Cleveland, Mississippi, a Republican town later this year.

But growth or not, there is a problem, opponents of the president say.

'MORE WE DON'T KNOW'

The sheer fact that Trump could profit from his presidency and that foreign governments could patronize The Trump Organisation to curry favour, is enough to create innumerable conflicts of interest, said Evers.

In a lawsuit filed in June, nearly 200 Democratic members of Congress cited examples of favours accorded by foreign governments to the Trump Organisation, including long-sought trademarks approved in China.

They demand that any foreign income or contract should be submitted to Congress for approval, in keeping with the emoluments clause of the US Constitution.

"If President Trump believes that his receipt of foreign emoluments raises no corruption concerns, he simply needs to present them to Congress - which his party controls - and get approval before he accepts them," said Connecticut's Democratic Senator Richard Blumenthal, who spearheaded the lawsuit.

"The fact that he has refused to take that step - thumbing his nose at the Constitution - raises serious questions about what he is trying to hide."

The Trump Organisation is a family firm, is not listed on the stock exchange and as such does not release its earnings.

Trump has also always refused to release his tax returns, meaning that much is unknown about deals and finances.

Disclosures published in June by the Office of Government Ethics showed that Trump brought in around US$600 to US$650 million in assets and income over the last year.

His income at Mar-a-Lago, his Florida private members club nicknamed the "Winter White House," was up from US$30 to US$37 million.

"There is every reason to believe there is much more we don't know about, and it is probably the things we don't know about that are the most troubling," said Blumenthal.