Bruce Ohr Fought Russian Organized Crime. Now He’s a Target of Trump.

Mr. Ohr’s section supported the 2000 prosecution of Pavlo Lazarenko, the former prime minister of Ukraine, who was convicted of money laundering, wire fraud and extortion in a case brought by the office of the United States attorney in San Francisco at the time, Robert S. Mueller III, who is now the special counsel.

Mr. Ohr was a manager, not a litigator, who built bridges with law enforcement agencies around the world, former Justice Department officials said. He sent top deputies to Hungary to root out the nascent Russian mob in the early 2000s. F.B.I. agents viewed the commitment as a sign of his seriousness about combating Russian organized crime.

In 2006, Mr. Ohr was part of a group of government officials who revoked the visa of Oleg Deripaska, a Russian billionaire and aluminum magnate. Officials were concerned that Mr. Deripaska might try to come to the United States to launder illicit profits through real estate, a former law enforcement official said.

Mr. Deripaska, a close ally of President Vladimir V. Putin of Russia, has been tied to the former Trump campaign chairman Paul Manafort, who was convicted last week of tax and bank fraud. In 2016, Mr. Manafort offered private campaign briefings to Mr. Deripaska, raising concerns about the prospect of Russians wielding influence inside the White House. In April, the United States imposed sanctions on Mr. Deripaska.

In 2007, Mr. Ohr met Mr. Steele, who was still with MI-6, the British spy service, according to a former senior American law enforcement official who knows both men. Both governments approved their contacts, the former official said.

Mr. Ohr moved on to other senior jobs, starting in 2010 as counsel for international relations in the Justice Department’s transnational organized crime and international affairs section, where he bolstered partnerships with foreign law enforcement agencies. In 2014, he became the director of the Organized Crime Drug Enforcement Task Forces, distributing grant money to bolster prosecutorial work.