WASHINGTON — The mandate given to Robert S. Mueller III and his team was broad: to investigate not just Russian election interference but also any related crimes they might unearth. So when this group of seasoned prosecutors began rooting around Washington, they pounced on a ripe target — lobbyists taking millions of dollars from foreign governments.
At the trial of Paul Manafort, an unflattering picture has emerged of lawyers, lobbyists and consultants from both political parties winning big paydays for work on behalf of a Kremlin-aligned former Ukrainian strongman. Some spent the money on cars and homes, prosecutors said, and a jacket made of ostrich for Mr. Manafort.
The vigor with which Mr. Mueller has investigated the flows of foreign money from Ukraine, Turkey and other countries into Washington could be as much a part of his legacy as special counsel as whatever he discovers about possible collusion between Russia and the Trump campaign or presidential obstruction of justice.
The Manafort case is part of a broader inquiry into the lucrative work done on behalf the former president of Ukraine, Viktor F. Yanukovych, and Mr. Mueller has handed some elements of the investigation to prosecutors in Manhattan. Beyond the special counsel’s office, the Justice Department has also recently been pursuing foreign influence cases with greater urgency.
All of this has prompted lobbyists to hunt for advice about how to comply with laws governing that sphere, long viewed as toothless. “The phone rings much more often with this question than it did two years ago,” said Tom Spulak, a partner at the King & Spalding law firm who advises on lobbying compliance.
Over the past year, Mr. Mueller and the Justice Department have pursued numerous cases both under the Foreign Agents Registration Act, or FARA, and related to foreign influence operations more broadly. FARA prosecutions were once almost unheard-of, according to a Justice Department inspector general report: For nearly a half-century, from 1966 until 2015, the department pursued only seven.
In addition to Mr. Manafort, the recent cases include the special counsel’s indictments against Russians who disseminated stolen information and used disinformation to influence how Americans perceived the candidates in the 2016 presidential election. Also among them is the complaint against Maria Butina, the Russian accused of acting as a foreign agent and plotting to gain Republican support for pro-Russia policies.
Even the case against Michael T. Flynn, Mr. Trump’s former national security adviser, included allegations that he had lied to investigators about lobbying work he did on behalf of the Turkish government.
Taken together, the cases shine a light on foreign influence operations that have become deeply embedded in Washington, and the culture of lobbyists who get rich helping their foreign clients affect how laws and policies are made in the capital.
To be sure, federal law enforcement officials took a more aggressive stance on foreign influence before the appointment of Mr. Mueller. They increased enforcement of FARA as part of a move to do “everything we could to meet the counterintelligence mission of the Justice Department,” said David Laufman, the former chief of the department’s counterintelligence and export control section who oversaw the enforcement surge.
The department began to write more aggressively worded letters to lobbyists seeking information about their work. After receiving letters of inquiry from the Justice Department last year, four Russian news media companies, including RIA Global and RTTV America, have registered as agents of a foreign principal under FARA. In retaliation, Russia passed a law to designate international news media companies as foreign agents.
But because of the intense attention it has drawn, Mr. Mueller’s investigation shined a spotlight on the waves of foreign money washing through American politics in a way that the other Justice Department efforts never could.
The number of new primary FARA registrations grew to 102 in 2017 from 69 in 2016, and was on pace to rise again in 2018, according to figures from the Justice Department published by the law firm Holland & Knight.
The first days of Mr. Manafort’s trial offered exhibit after exhibit of this lavish world, beginning with his extravagant purchases, including cars, Persian rugs and expensive clothes.
It also revealed bipartisan largess. One 2014 email presented in court on Tuesday showed the Democratic consultant Thomas A. Devine proposing a “day rate” of $10,000 to do work in Ukraine on behalf of Mr. Yanukovych, the Russia-aligned former president who was a longtime client of Mr. Manafort.
“You would need to make the travel arrangements, and transfer the $50G before the trip,” he wrote to Rick Gates, Mr. Manafort’s partner for the Ukraine work. “If you want me to come on Monday and leave Thursday it would be $40G.”
Mr. Devine, who is known as Tad, went on to become the chief strategist for the presidential campaign of Senator Bernie Sanders of Vermont, a self-proclaimed democratic socialist.
In addition to the investigations of Mr. Manafort and Mr. Gates, who pleaded guilty in February to numerous financial crimes and became a cooperating witness in the special counsel investigation, Mr. Mueller’s team pursued three other investigations into lawyers and lobbyists who did work in Ukraine.
The cases involve Gregory B. Craig, who served as the White House counsel under President Barack Obama before leaving to work for the law firm Skadden, Arps, Slate, Meagher & Flom; Tony Podesta, an influential Washington lobbyist whose brother, John D. Podesta, was chairman of Hillary Clinton’s presidential campaign; and former Representative Vin Weber, Republican of Minnesota, who joined the lobbying firm Mercury Public Affairs after leaving Congress.
None have been charged with any crimes. Mr. Mueller’s referral of those cases several months ago to federal prosecutors in New York was revealed in news reports on Tuesday.
Whereas the public once thought of the Justice Department’s counterintelligence mission as primarily trying to catch foreign spies seeking to obtain government secrets, the department has made clear in a recent cybercrimes report and congressional testimony that influence has become as great a threat.
The government’s case against Ms. Butina, which was not brought under FARA, could be a template for future prosecutions, said a former Justice Department official, who predicted they could spread to influence peddling from Eastern Europe and China as well as Russia.
Ms. Butina was charged with acting as a Russian agent, a more serious crime than a typical FARA violation. The charge allowed prosecutors to impanel a grand jury and issue subpoenas to subjects of investigations — tools not available in FARA inquiries. Bills to give the Justice Department the power to compel records in FARA cases are sitting in Congress but have gained little traction.
The lobbying industry last faced intense scrutiny after the Republican lobbyist Jack Abramoff was caught up in a sprawling corruption and bribery investigation. He went to jail in 2006 for fraud. That case put a temporary chill on the industry, and some Washington lobbyists made up for lost business with foreign clients trying to exert influence on American politicians.
The Justice Department will continue to pursue foreign influence operations inside the United States, the deputy attorney general, Rod J. Rosenstein, vowed last month.
Russian schemes to influence the presidential election, he said, are “just one tree in a growing forest.”