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.
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. ...
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. ...