Tony Podesta, 74, built one of the highest-grossing lobbying firms in Washington, signing clients across industries and ideologies — including defense contractors like Lockheed Martin, banks like Wells Fargo, drug makers like Mylan and foreign regimes like the government of the former Egyptian dictator Hosni Mubarak. Tony Podesta is known for his fund-raising — in 2016, he donated or raised nearly $900,000 for Mrs. Clinton’s campaign and the Democratic Party — as well as for a lavish lifestyle.

Had Mrs. Clinton prevailed, as official Washington expected, it most likely would have cemented the legacies of both brothers — John Podesta as a key confidant to presidents and one of the most important Democratic strategists of the past century, and Tony Podesta as the go-to lobbyist for Democratic administrations. Instead, the Podestas have been drawn into the vortex of investigations and conspiracy theories that have enveloped Washington in the Trump era.

Tony Podesta stepped down from his firm hours after it was obliquely referenced in the indictments of Mr. Manafort and Mr. Gates, though he had been in talks about leaving for months. It is unclear what will happen to his investment in the Podesta Group, which has been hemorrhaging clients and employees, both because of the mounting scrutiny and because businesses are looking for lobbyists with connections to the Trump administration, according to interviews and lobbying filings. Some firm partners are starting a new firm next month called Cogent Strategies, in which Tony Podesta will have no stake.

Last week’s indictment did not name the Podesta Group or another firm with which it worked on the Ukraine account, Mercury Public Affairs. Instead, the indictment referred to them as “two Washington, D.C., firms” that were recruited by Mr. Manafort and Mr. Gates.

While both firms disclosed the work to Congress under less-rigorous domestic lobbying rules, they did not initially register under the Foreign Agents Registration Act. The indictment alleges that was done intentionally — by routing the money through a Brussels-based nonprofit — “to minimize public disclosure of their lobbying campaign” that “was under the ultimate direction” of Mr. Yanukovych, his party and his government.

Tony Podesta and his lawyers are working to navigate the issues raised by the Mueller investigation and accompanying attacks from the right. They have already demanded a retraction from the conservative news media on claims that both Podestas worked with Mr. Manafort to advance Russian interests.