Former Trump campaign chairman Paul Manafort parted ways with WilmerHale, the law firm defending him, earlier this week. That was largely because Bob Mueller’s 16-lawyer Russia probe—which is targeting him—has shifted its focus and is drilling down on tax issues, which aren’t WilmerHale’s specialty. But the parting of ways with WilmerHale was also in part because Manafort’s finances are increasingly strained, according to sources familiar with the situation.

“Paul Manafort’s resolve is limitless, but his resources are not,” said a person close to Manafort.

Manafort isn’t the only person facing financial challenges because of the legal costs of responding to Mueller’s probe. Michael Flynn, the retired general and deposed National Security Adviser, is struggling mightily with his mounting legal bills, according to a source familiar with his situation. The expenses has put his family’s finances under significant duress, the source said, and it’s expected he will soon create a legal defense fund to keep from going bankrupt.

Hiring the high-powered Washington lawyers necessary to respond to a deep-dive Justice Department investigation can be extraordinarily costly. And Manafort—despite his past lucrative contracts with foreign governments, and despite the fact that he owns numerous properties around the country—is feeling the pinch. Sources say that’s part of the reason he is no longer retaining WilmerHale; the firm is known for handling Congressional investigations, but Mueller’s probe has now shifted its focus to international tax issues—which meant Manafort needed lawyers with that expertise. So he has brought in Miller Chevalier, a boutique Washington law firm full of international law experts, and has parted with WilmerHale.

David Rivkin, a longtime conservative Washington attorney who worked in the Justice Department under Ronald Reagan and George H. W. Bush, said Mueller’s probe is undoubtedly straining the finances of all its targets.

“It’s obvious that it has morphed into an open-ended investigation that is way beyond the Russian collusion, and the only unifying principle seems to be that it covers people who are close to Trump or worked with Trump,” he said. “And that is a classical definition of a fishing expedition.”

Mueller’s legal team has 16 attorneys, as well as other support staff, and it’s funded by the Justice Department. Mueller’s team includes former federal prosecutors with broad-ranging areas of expertise who are highly motivated and aggressive.

“It obviously has a deleterious effect on both people’s professional lives—in terms of their ability to carry out their jobs—but also on a personal level,” Rivkin continued. “People who are being severely financially stressed by this investigation.”