When Senator Robert Menendez arrived in Qatar in 2022 to attend the country’s lavish production of the men’s soccer World Cup, he gave an unusual interview to the authoritarian government’s news agency praising the progress that Qatar had made on labor rights.

The tiny Gulf state was facing an onslaught of international criticism over its preparations for the world’s biggest sporting event, including over the exploitation of migrant workers who built the tournament’s infrastructure. But Mr. Menendez, a New Jersey Democrat, said he preferred to highlight positive aspects of the games, and the host nation.

Traveling to Qatar gave Mr. Menendez “the experience to say wow!” he said, according to the Qatari state news agency. “My short visit to Doha was joyful and I saw that the global community came to Qatar and were well received and well respected.”

Less than a year later, Mr. Menendez, 70, was charged in a federal indictment with taking hundreds of thousands of dollars in bribes, including bars of gold, to wield his power at home and abroad. The case initially focused on actions that benefited Egypt. But on Tuesday, updated court documents added new details related to Qatar.

In the updated indictment, prosecutors accused Mr. Menendez of using his influence and connections — a byproduct of his powerful position as the chairman of the Senate Foreign Relations Committee — to help a New Jersey developer get financial backing from an investment fund run by a Qatari royal family member in exchange for lucrative bribes.

To help win over the Qataris, prosecutors said, the developer, Fred Daibes, also expected Mr. Menendez to “take action to benefit the government of Qatar.”

The Qatari government did not respond to a request for comment on the accusations in the Menendez case. Mr. Daibes’s lawyer, Tim Donohue, said he had no comment. Adam Fee, a lawyer for Mr. Menendez, said Tuesday that the senator’s contacts with foreign officials were “routine” and “lawful.” Mr. Menendez and Mr. Daibes have pleaded not guilty.

And while the indictment does not accuse the Qatari government or the Qatari royal family member of illegal activity, it is the latest in a line of cases in which Qatar, a major natural gas exporter, has appeared to seek greater influence in the United States and Europe by forging relationships with powerful government officials, or people connected to them.

On Tuesday — the same day that the updated indictment was released — Barry Bennett and Doug Watts, Republican political consultants, admitted in court filings to violating American foreign influence rules over their lobbying activities on behalf of Qatar. That case came just over a year after Belgian authorities announced charges against a vice president of the European Parliament, saying that she had traded political decisions benefiting Qatar for bags of cash.

Qatar, shadowed for years by accusations it had used bribery to win the World Cup hosting rights, has denied that it sought to influence the European official, who has also maintained her innocence.

To analysts who study the Gulf, though, such cases are pieces of a broader picture, and a window into how the region’s fossil fuel-rich states transform their wealth into political power around the world.

Over the past two decades, the rulers of Qatar, a nation with a population of less than 400,000 citizens but a sovereign wealth fund that controls $475 billion in assets, have used some of the state’s wealth to thrust their conservative Islamic country into the global spotlight. Qatar is home to a U.S. military base, a major international airline, one of the world’s largest sports broadcasters and the Al-Jazeera news network, which projects its worldview to vast Arabic and English-speaking audiences. Qatar has also positioned itself as an essential mediator with the ability to serve as a link between Western governments and difficult parties, including Hamas, Iran, Russia and the Taliban.

Most recently, Qatar has played a key role in negotiations to release hostages held by Hamas, the Palestinian armed group that launched the Oct. 7 attacks in Israel, and to reach a cease-fire in the war in Gaza.

The government’s efforts to increase its international relevance — particularly to key allies like the United States — are partly motivated by Qatar’s vulnerabilities, analysts say. Qatar is a peninsula flanked by much larger regional powers: Saudi Arabia and Iran.

In 2017, Saudi Arabia, the United Arab Emirates, Bahrain and Egypt severed ties with Qatar, accusing its government of supporting Islamic extremism and terrorism and meddling in their internal affairs. Saudi Arabia closed Qatar’s only land border, effectively isolating the country, which scrambled to find new sources of essential goods.

“When the blockade began in June 2017, Qatar found itself on the back foot when it came to power and influence in Washington, in contrast to Gulf neighbors Saudi Arabia and the U.A.E.,” said Anna Jacobs, a senior Gulf analyst for the International Crisis Group who is based in Doha, the Qatari capital.

The rift was repaired gradually beginning in 2021 — Saudi Arabia and Qatar now have relatively warm relations — but “this vulnerability pushed Qatar to focus on network building and developing a stronger presence in Washington to protect its interests,” Ms. Jacobs said.

Gulf countries like Qatar view cultivating relationships with politicians like Mr. Menendez as a sort of “cynical statecraft,” said Hussein Ibish, a senior resident scholar at the Arab Gulf States Institute in Washington. Like many Washington think tanks, his research organization has received funding from Saudi Arabia and the United Arab Emirates — a sign of the depth of Gulf influence in the United States.

When the rift between Qatar and its neighbors began, “the perception in Doha was that Saudi and Emirati officials had invested heavily in building relationships not only with members of the Trump administration but also in their lobbying activities in the United States, and that Qatar needed to do the same,” said Kristian Coates Ulrichsen, a Middle East fellow at Rice University’s Baker Institute for Public Policy.

The allegations in Mr. Menendez’s indictment related to Qatar stretch from December 2020 until last year. At the time, Mr. Daibes was seeking financing for a real estate project in New Jersey, and Mr. Menendez introduced him to a Qatari investor who was a member of the country’s royal family. The royal’s fund had “ties to the government of Qatar,” the indictment said.

While the Qatari was considering the investment, Mr. Menendez “made multiple public statements supporting the Government of Qatar” and asked Mr. Daibes to share those statements with the investor and an unnamed Qatari government official.

“You might want to send to them. I am just about to release,” Mr. Menendez wrote in a message to Mr. Daibes in 2021, attaching the text of a pending statement. That day, his office issued a news release praising Qatar for agreeing to host Afghans seeking refuge in the United States.

Soon after, the Qatari investor messaged the Qatari official: “I received copy from F,” according to the indictment. “F” appeared to be a reference to Mr. Daibes.

A month later, prosecutors said Mr. Daibes texted the senator photos of several luxury wristwatches and asked, “How about one of these.”

The Qatari company eventually invested tens of millions of dollars into Mr. Daibes’s real estate project.

The indictment does not name the Qatari investor, the Qatari investment company, or the Qatari government official.

But deed records in Bergen County, New Jersey, show that in 2023, a London-based company entered into a $45 million shared-ownership agreement for a New Jersey real estate project with Mr. Daibes. That company — Heritage Advisors — was founded by a member of Qatar’s royal family, Sheikh Sultan bin Jassim Al Thani.

Heritage Advisors did not respond to an email and a phone call seeking comment from the company and Sheikh Sultan. Efforts to reach Sheikh Sultan via his Qatar-based holding company, Al-Alfia, were also unsuccessful.

The royal family is a sprawling extended clan, but its members often intermarry and are closely knit. Before entering business, Sheikh Sultan worked for Qatar’s ministry of finance and petroleum. He later worked in the office of Qatar’s deputy prime minister and was the head of Qatar’s Tourism Authority, according to a biography on Heritage’s website.

It is unclear what benefits Mr. Menendez might have provided to Qatar beyond rosy public statements, but he was not the country’s only friend in Washington: Qatar has also sought to cultivate relationships with think tanks, scholars and journalists, and it foots much of the bill for the Al Udeid Air Base, which hosts the forward headquarters of the U.S. Central Command.

“What they want from the United States is protection,” said Mr. Ibish, the scholar with the Arab Gulf States Institute. “They need external support from a great power because they have a very tense relationship with so many of their most important neighbors.”