WASHINGTON — As Donald J. Trump was preparing to deliver an address on energy policy in May 2016, Paul Manafort, his campaign chairman, had a question about the speech’s contents for Thomas J. Barrack Jr., a top campaign fund-raiser and close friend of Mr. Trump.
“Are you running this by our friends?” Mr. Manafort asked in a previously undisclosed email to Mr. Barrack, whose real estate and investment firm does extensive business in the Middle East.
Mr. Barrack was, in fact, coordinating the language in a draft of the speech with Persian Gulf contacts including Rashid al-Malik, an Emirati businessman who is close to the rulers of the United Arab Emirates.
The exchanges about Mr. Trump’s energy speech are among a series of interactions that have come under scrutiny by federal prosecutors looking at foreign influence over his campaign, his transition and the early stages of his administration, according to documents and interviews with people familiar with the case.
Investigators have looked in particular at whether Mr. Barrack or others violated the law requiring people who try to influence American policy or opinion at the direction of foreign governments or entities to disclose their activities to the Justice Department, people familiar with the case said.
The inquiry had proceeded far enough last month that Mr. Barrack, who played an influential role in the campaign and acts as an outside adviser to the White House, was interviewed, at his request, by prosecutors in the public integrity unit of the United States attorney’s office in Brooklyn.
Mr. Barrack’s spokesman, Owen Blicksilver, said that in expectation of this article, Mr. Barrack’s lawyer had again contacted the prosecutors’ office and “confirmed they have no further questions for Mr. Barrack.”
Mr. Barrack has not been accused of wrongdoing, and his aides said he never worked on behalf of foreign states or entities. Asked about the status of the inquiry, a representative for the United States attorney’s office in Brooklyn declined to comment.
The relationship between Mr. Barrack, Mr. Manafort and representatives of the U.A.E. and Saudi Arabia, including Mr. al-Malik, has been of interest to federal authorities for at least nine months. The effort to influence Mr. Trump’s energy speech in 2016 was largely unsuccessful.
The special counsel’s two-year investigation into Russian interference in the 2016 presidential election has ended and federal prosecutors in Manhattan have signaled that it is unlikely they would file additional charges in a separate hush money investigation that ensnared members of Mr. Trump’s inner circle.
But as the scrutiny of Mr. Barrack indicates, prosecutors continue to pursue questions about foreign influence. Among other lines of inquiry, they have sought to determine whether Mr. Barrack and others tried to sway the Trump campaign or the new administration on behalf of the United Arab Emirates and Saudi Arabia, two closely aligned countries with huge stakes in United States policy.
Between Mr. Trump’s nomination and the end of June, Colony Capital, Mr. Barrack’s real estate investment and private equity firm, received about $1.5 billion from Saudi Arabia and the United Arab Emirates through investments or other transactions like asset sales, Mr. Barrack’s aides said. That included $474 million in investment from Saudi and Emirati sovereign wealth funds, out of $7 billion that Colony raised in investment worldwide.
An executive familiar with the transactions had provided The New York Times with somewhat different figures last year.
Investigators have also questioned witnesses about Mr. Barrack’s involvement with a proposal from an American group that could give Saudi Arabia access to nuclear power technology. And they have asked about another economic development plan for the Arab world, written by Mr. Barrack and circulated among Mr. Trump’s advisers.
Aides to Mr. Barrack, who is of Lebanese descent and speaks Arabic, said he had always acted as an independent intermediary between Persian Gulf leaders and the Trump campaign and administration, never on behalf of any foreign official or entity.
“The ideas he was giving voice to were his ideas,” said Tommy Davis, Mr. Barrack’s former chief of staff, who continues to work for him. “These are ideas that he has been advocating for decades.”
He said Mr. Barrack had no incentive to lobby on behalf of any particular country or countries in the Persian Gulf because his business interests and policy concerns span the entire region and countries at odds with one another.
Nor is there any evidence, Mr. Barrack’s aides said, that either Mr. Barrack or his Los Angeles-based company has profited from his efforts.
“There is zero pay to play here,” Mr. Blicksilver, Mr. Barrack’s spokesman, said. “That is supported by the facts and the numbers.”
For Mr. Barrack, 72, the inquiry has unfolded amid a series of other setbacks. A friend of Mr. Trump since the 1980s, he had anticipated that his efforts to elect Mr. Trump, help run his transition team and manage his inauguration would land him a prominent role in the administration.
But Jared Kushner, the president’s son-in-law, blocked Mr. Barrack from becoming a special envoy to the Middle East. A proposed role as a kind of superambassador to Central and South America did not materialize either.
At the same time, Colony Capital encountered substantial difficulties after a troubled merger drove down its stock price and forced a series of management changes.
Mr. Trump’s inauguration in January 2017 was a high point for Mr. Barrack: The inaugural committee he led set records for the amount of money raised and spent to celebrate an inauguration.
But critics claimed the inaugural became a hub for peddling access to foreign officials and business leaders, or people acting on their behalf. The United States attorney’s office in Manhattan opened an investigation into possible violations of campaign finance law, focusing partly on whether foreigners, who were barred from contributing to the $107 million inaugural fund, illegally funneled donations through Americans.
Questions about whether Mr. Barrack complied with the Foreign Agents Registration Act, commonly known as FARA, arose during the Russia inquiry led by the special counsel, Robert S. Mueller III, and were referred to the United States attorney’s office in Brooklyn.
Three of the six former Trump aides who were charged by the special counsel acknowledged violating the foreign lobbying statute in their guilty pleas: Mr. Manafort, Rick Gates, who served as deputy campaign chairman for Mr. Trump in 2016, and Michael T. Flynn, Mr. Trump’s former national security adviser.
But while the Justice Department has been trying for several years to step up criminal enforcement of FARA requirements, such cases are typically difficult to prove. “Are you acting under someone’s direction or control?” Adam S. Hickey, the deputy assistant attorney general in charge of the national security division, said in a recent interview. “Are you working on their behalf? That can be a very hard thing to investigate or to decide.”
Central to the inquiry into Mr. Barrack are his dealings with Mr. al-Malik, who is well connected in the court of Crown Prince Mohammed bin Zayed, the de facto ruler of the United Arab Emirates widely known by his initials, M.B.Z., and is close to the prince’s brother, Sheikh Hamdan bin Zayed, who oversees the United Arab Emirates’ intelligence services. Sheikh Hamdan is considered to be Mr. al-Malik’s patron and a major financier of his business activities.
When Mr. Trump was elected, Mr. al-Malik received a coveted invitation to the inaugural’s most exclusive event — the chairman’s dinner, hosted by Mr. Barrack.
In early 2018, Mr. al-Malik gave an interview and provided documents to federal prosecutors who questioned whether he had been acting as an unregistered foreign agent in the United States, according to two people familiar with the matter. After he was interviewed, Mr. al-Malik left for the United Arab Emirates and has not returned to the United States.
William F. Coffield, a lawyer for Mr. al-Malik, said that he “voluntarily cooperated with the special council’s office,” adding, “They accepted his cooperation and they certainly aren’t going after him.”
Investigators have documented a string of instances in which Mr. Barrack appears to have tried, with feedback from Mr. al-Malik and others, to shape the message of the Trump campaign or new administration in ways that were more friendly to Middle East interests.
Although he was not always successful, Mr. Barrack had substantial sway within the campaign when it was overseen by Mr. Manafort, a longtime friend, and Mr. Manafort’s deputy, Mr. Gates.
Mr. Barrack recommended that Mr. Trump hire Mr. Manafort, who rose to campaign chairman before he was fired over a separate foreign lobbying scandal. Mr. Manafort, who was awash in debt and had no income, had hoped that after the campaign Mr. Barrack would use his deep ties to the oil-rich nations to drum up business for them both, according to people familiar with the situation.
In one email to the U.A.E.’s ambassador in Washington, Mr. Barrack promoted Mr. Manafort as someone who was “totally programmed” on the alliance between the Saudis and Emiratis.
Mr. Manafort, in turn, was willing to describe Mr. Barrack to foreign officials as someone who could speak for the campaign on all subjects.
The Times learned of some of Mr. Barrack’s electronic correspondence from people critical of Emirati foreign policy and from people familiar with his work with the Trump campaign.
In early May 2016, Mr. Barrack asked Mr. al-Malik and other Persian Gulf contacts to propose language for a draft of an energy speech that Mr. Trump was to deliver in Bismarck, N.D., that month.
Mr. Barrack’s draft of the speech cited a new generation of leaders in the Gulf region, naming both the Emirati crown prince and his ally, Mohammed bin Salman, then deputy crown prince of Saudi Arabia. The Saudi prince, often referred to by his initials, M.B.S., has now consolidated his control of the kingdom.
Mr. Barrack’s aides said he tried to influence Mr. Trump’s address because he cares deeply about United States relations with the Persian Gulf region and was worried that Mr. Trump’s inflammatory campaign messaging would damage them. Among other provocative statements, Mr. Trump had vowed that, if elected, he would bar Muslims from entering the United States.
When Mr. Trump and a campaign speechwriter rejected Mr. Barrack’s draft, Mr. Manafort wrote to Mr. Barrack, “Send me an insert that works for our friends and I will fight for it.”
In the end, to Mr. Barrack’s disappointment, Mr. Trump made only a passing reference to the need to work with “gulf allies” on “a positive energy relationship as part of our antiterrorism strategy.”
A few days later, Mr. Manafort emailed Mr. Barrack that “on the platform issue there is another chance to make our gulf friends happy.” He was referring to language in the Republican Party platform to be approved at the convention where Mr. Trump would formally become the nominee.
In late June, Mr. Manafort alerted Mr. Barrack that Mr. Trump had softened his stance on a Muslim ban. Mr. Barrack quickly forwarded the email to Yousef al-Otaiba, the Emirates’ powerful ambassador in Washington.
Then in July, Mr. Barrack informed Mr. Otaiba that the Trump team had removed language from the proposed Republican platform that would have called for the disclosure of redacted pages related to Saudi Arabia in a report on the Sept. 11, 2001, terrorist attacks on the United States.
“Really confidential but important,” he wrote, enclosing campaign emails on the subject. “Please do not distribute.”
Two days later, Congress released the passages, which detailed contacts between Saudi officials and some of the hijackers.
Mr. Barrack tried to set up a meeting that summer between Mr. Manafort and Mohammed bin Salman, the Saudi deputy crown prince, but it was canceled at the last moment.
The month after Mr. Trump clinched the Republican nomination, Mr. Barrack traveled to the Persian Gulf and met with the Saudi prince and the Emirati crown prince, aides said. At a dinner meeting in Saudi Arabia, he was briefed on the kingdom’s economic plan.
In a subsequent text to Mr. Manafort, Mr. Barrack sounded elated.
“Amazing meetings. Off the map,” he wrote. “A lot to talk about and do.”