When the president-elect's son Eric Trump jetted to Uruguay in early January for a Trump Organization promotional trip, U.S. taxpayers were left footing a bill of nearly $100,000 in hotel rooms for Secret Service and embassy staff.

It was a high-profile jaunt out of the country for Eric, the fresh-faced executive of the Trump Organization who, like his father, pledged to keep the company separate from the presidency. Eric mingled with real estate brokers, dined at an open-air beachfront eatery and spoke to hundreds at an "ultra exclusive" Trump Tower Punta del Este evening party celebrating his visit.

The Uruguayan trip shows how the government is unavoidably entangled with the Trump company as a result of the president's refusal to divest his ownership stake. In this case, government agencies are forced to pay to support business operations that ultimately help to enrich the president himself. Though the Trumps have pledged a division of business and government, they will nevertheless depend on the publicly funded protection granted to the first family as they travel the globe promoting their brand.

A spokeswoman for Eric Trump declined to make him available for an interview and did not provide answers to a list of detailed questions about the trip.

Eric Trump's trip in early January to the coastal resort town appeared to be brief - perhaps as short as two nights, according to a review of local press clips and social media.

The bill for the Secret Service's hotel rooms in Uruguay totaled $88,320. The U.S. Embassy in Montevideo, the capital city of Uruguay, paid an additional $9,510 for its staff to stay in hotel rooms to "support" the Secret Service detail for the "VIP visit," according to purchasing orders reviewed by The Washington Post.

"This is an example of the blurring of the line between the personal interest in the family business and the government," said Kathleen Clark, an expert on government ethics and law professor at Washington University in St. Louis.

Despite the use of public funds, government agencies would not provide key details connected to the trip, including the duration of the stay, the name of the hotel or the number of booked rooms. A spokesman from the Secret Service, citing security concerns, declined to comment.

The money for the hotel rooms was paid through the State Department, but a spokesman there declined to comment on the trip. She instead referred reporters to the White House and back to the Secret Service, whose spokesman once again declined to comment. The White House also did not respond to requests for comment.

"There is a public benefit to providing Secret Service protection," Clark said. "But what was the public benefit from State Department personnel participating in this private business trip to the coastal town? It raises the specter of the use of public resources for private gain."

Immediate family members of presidents have for decades been guaranteed taxpayer-funded safeguards, and their safety is paramount to national security, especially as they travel to foreign and potentially dangerous hot spots.

In 1917, Congress first authorized the then-Secret Service Division of the U.S. Treasury Department to protect the immediate family of the president. In 1984, a statute extended that protection for other key individuals, including the immediate family of the vice president.

Presidents George W. Bush and Bill Clinton even authorized Secret Service protection for their adult daughters for an unspecified period of time after the presidents left office.

"The Secret Service does not have an option as to when it is, where it is, nor as to how much it costs, and whether it's domestic or international," said W. Ralph Basham, former director of the service. "Think about the consequences of something happening to one of the children. The security of it outweighs the expenses of it."

While Eric Trump was in Uruguay, the full presence of U.S. security operations did not go unnoticed by the local media and paparazzi.

La Nación, an Argentine publication, began its article about the visit with a scene-setter describing two Secret Service agents inside the Punta del Este showroom. Four more agents tried, unsuccessfully, to blend in with the crowd of real estate buyers outside, La Nación wrote.

A local photographer encountered Eric Trump at La Huella, a restaurant described as the "ultimate in chic beach eating" and renowned for its grilled seafood entrees.

"He had lunch there for about an hour and a half with some friends and acquaintances," photographer Cristian Cordoba said in an email to The Post. "Secret Service was very close by monitoring. He was very kind and courteous with everyone that wanted to say hi to him. He even shook my hand after I took his picture. He said he loved the food and the place and would love to come back."

A well-known pop singer from Argentina, Maxi Trusso, performed at the Punta del Este party honoring Eric Trump. Trusso later told the local press that he wrote a song about Donald Trump at Eric's request. Trusso titled the composition "Free and Stronger." He also said that he was invited to sing at the inauguration but declined the offer.

The Trumps, who do not own the Punta del Este project, licensed their name to its developers, who have paid Trump's company between $100,000 and $1 million, according to Trump's financial disclosure filing in May.

The 26-story tower is under construction. Its condos - which start at $550,000 and climb to $8 million - are expected to be finished in late 2018. Tower advertisements list amenities including waterfall pools, a massage room and a private theater.

The developer, YY Development Group, did not respond to requests for comment. But the chief executive, Juan Jose Cugliandolo, told the Associated Press last month that two-thirds of the condos were sold. Cugliandolo said of Eric Trump's trip, "It honors us that he would come this summer, days before his father takes office," the Associated Press reported.

During an interview on the trip, Eric Trump fielded questions from the local media about political issues, including the president of Argentina and how his policies had affected the Trump property in Uruguay.

"I don't speak politics," he said, according to a video of the interview. "It's not my world. I'm a business guy."

But the reporter pressed again, and Eric Trump said that he had a favorable opinion of Argentina's president for "opening up the country," which had helped business and helped the economy of Uruguay and Argentina.

He was also asked about his father and if he would ever join the administration. Eric Trump told La Nación that the relationship between the Trump Organization and his father's administration would be completely separate, like "church and state."

But ethical experts say that the steps Donald Trump announced to facilitate such a separation, including placing his business into a trust overseen by Eric, Donald Trump Jr. and a longtime company executive, are not enough to eliminate concerns about conflicts of interest.

"Having refused to sever his own personal financial interests, [the president] is now sending his emissaries, his sons, out to line his own pockets, and he's subsidizing that activity with taxpayer dollars," said Norm Eisen, a former President Barack Obama administration ethics adviser who is part of a lawsuit accusing Trump of violating a constitutional provision barring presidents from taking payments from foreign governments.

It is unusual, although not unprecedented, for trips of presidential family members to focus on the development of private moneymaking opportunities.

In 1989, Jeb Bush drew criticism after he traveled to Nigeria on a business trip less than two months after his father, George H.W. Bush, was sworn in as president.

"The president's children should not be deprived of career opportunities just because they are members of the first family," the White House press secretary said in 1989.

Jeb Bush, through his spokeswoman, declined an interview request.

During his interview with the media in Uruguay, Eric was asked about how his life would change under his father's administration.

"We're going to have an amazing company, and he's going to do amazing things for the United States," he said to the local media. "He's going to be an incredible commander in chief. And I'm not going to be involved in politics, and he's not going to be involved in the business."

He also said that once his father moved to Washington, he would be headed back to New York to run the company with his brother. But there are early signs that Eric and Don Jr. will be spending plenty of time in Washington.

Several days ago, the brothers sat side-by-side in the front row during Trump's White House announcement of Neil Gorsuch as his nominee for the U.S. Supreme Court. Afterward, Don Jr. posted on social media that he had enjoyed chatting with Gorsuch about their shared love for fly-fishing.

Later this month, Eric and Don Jr. are expected to travel to Vancouver in celebration of the grand opening of the new Trump International Hotel & Tower.

The trip is expected to bring the Trump brothers together with wealthy Malaysian developer Tony Tiah Thee Kian and his son, Joo Kim Tiah, head of the Vancouver project.

Richard Painter, a former chief White House ethics lawyer for President George W. Bush who joined Eisen in the lawsuit, called the family's Secret Service protection a "worthwhile expenditure of taxpayer money." But Painter said he worried that it could be misread as boosting the Trump brand.

"All of this has an air of legitimacy: The connection to the U.S. government, and the suggestion that if you do business with this company you'll ingratiate yourself with the Trump administration," Painter said. The implication is "if you do a good deal with us, you'll be in good with the United States. And the Secret Service presence just exacerbates that."

Jonnelle Marte and Carol Leonnig and staff researchers Alice Crites and Julie Tate contributed to this report.