Former National Security Adviser Michael Flynn plans to spend more than a million dollars on his legal defense, a source familiar with the situation told The Daily Beast on Monday. But because of the structure of the fund he has set up to pay for it, the public won’t know who is footing the bills.

The retired Army lieutenant general is facing legal scrutiny as part of an ongoing federal probe into alleged Russian government meddling in the 2016 presidential election. He’s now searching for ways to pay the resulting legal bills, including through a crowdsourcing effort he announced on Twitter on Monday morning.

“We deeply appreciate the support of family and friends across this nation who have touched our lives,” Flynn wrote.

Flynn is dealing with a multitude of potentially complex legal problems stemming from the Russia investigation, which has expanded to examine the private business activities of a number of current and former Trump aides and associates, including Flynn’s advocacy on behalf of a Turkish government-linked company last year. He belatedly disclosed that work under a federal law governing domestic lobbying and public relations on behalf of foreign governments and political parties.

According to the source, the legal defense fund Flynn established is legally structured as a trust—not a corporation, nonprofit, or political organization. Because Flynn is no longer in government service, he is not legally required to disclose the sources of funds placed in the trust, and Flynn does not plan to do so, the source said.

The legal defense fund’s website says it will not accept contributions from foreign nationals, but there are few legal boundaries to its fundraising practices, and the lack of disclosure will make it difficult to determine whether the fund is abiding by its stated donor restrictions. The source also said that the fund will not accept contributions from, or made at the behest of, the Trump Organization or the Trump presidential campaign, though Flynn’s attorney, Covington & Burling’s Robert Kelner, declined to speak on the record about that practice or other fundraising restrictions.

Without the assistance of foreign nationals or Trump-allied companies or individuals, Flynn will have a harder time scrambling for the cash. His large public profile should help with that. Other, lesser known aides, are less fortunate.

Michael Caputo, a former Trump campaign official who has been questioned by the House Intelligence Committee regarding Russia, told The Daily Beast it’s very safe to estimate that Flynn’s legal expenses will exceed $1 million. He said he interviewed numerous Washington attorneys who specialize in Congressional probes to represent him, and they all billed at least $1200 per hour.

Caputo said anyone testifying before a Congressional committee under these circumstances would need to practice, or “moot,” their hearing at least once. That practice session would take at least four hours, and would likely involve at least two attorneys, both of whom would bill $1200 or more for each hour. So just to do the bare minimum level of practice for one Congressional committee hearing, someone could expect to spend $10,000. Someone in Flynn’s situation could expect to face multiple committee hearings, and to have multiple practice sessions with multiple lawyers present for each hearing. The legal bills pile up fast.

On top of that, Caputo said people facing questions from Mueller’s team can expect exponentially higher bills. They will likely have lengthy question-and-answer sessions with members of the special counsel’s team, and have to answer document requests that could be complex and time-consuming.

“Somebody who’s a target can count on spending more than a million bucks,” Caputo said, “because they’ll be in the House and Senate jackpot and they’ll be in front of the Special Counsel.”

As of August 1, Caputo said he’s spent $30,000 on legal fees and other associated expenses—and that was just to take questions from one Congressional committee. He said he hasn’t heard from Mueller’s team. Caputo left the Trump campaign in June 2016, and isn’t facing questions about potential obstruction of justice related to the Comey firing.

“The fact of the matter is, if somebody like myself––who left the campaign in June––is enduring these dramatic expenses, you can imagine what’s happening to people who stayed with the president through the campaign until today,” he said.

Aides from past administration’s have faced daunting bills as well, even when they’re not the ones under direct scrutiny. Matt Schlapp, who served in the George W. Bush administration’s political affairs shop, said he ended up dolling out six-figures to white collar lawyers for help on a wide variety of testimonies he had to give to investigators. The financial burden was heavy. So was the psychological one.

“You have to scan all your emails, which is a frightening experience because it hits you how many you send in the course of a day,” he recalled. “You don’t sleep very well. You worry about hurting your friends…. It is generally a very stressful situation. But if you’re going to a grand jury or a House and Senate oversight hearing, this is not a time for your B-level traffic attorney. You have to go with the real deal because you’re looking at your whole career in front of you.”

Stan Brand, a longtime D.C. Attorney estimates that he had represented “half a dozen or more” White House aides who found themselves under legal jeopardy, including a young communications aide who went on to great things in television.

“On a saturday in March [1993], Bob Fisk, who was the independent counsel, laid a subpoena on the White House and dozens of people. It was shell shock. And so they all had to run off and get lawyers and George [Stephanopoulos] got me,” Brand recalled. “He said he was bright eyed and bushy-tailed coming to the White House and somehow he was now hiring a criminal defense lawyer.”

Brand moderated his fees to help Stephanopoulos with the cost. But it still added up to over $100,000. “And that was chicken feed compared to others,” Brand said. “And in those days, because of the independent counsel statute, you could seek reimbursement if you weren’t charged. But that was hard. You didn’t get all of it and some people didn’t get it.”

Flynn isn’t operating under that same statute. What he spends he is very unlikely to get back. He also benefits from not being a government employee right now, which Brand notes would make his legal benefactors subject to bribery statutes.

While Flynn has hired a top lawyer, his family is taking the lead in setting up the trust. His sister, Barbara Redgate, is listed as its trustee, and his brother, Joe Flynn, registered an alternate domain name for the trust’s website. Joe Flynn referred questions to Kelner.

Flynn’s son, Michael Flynn Jr., is also facing legal scrutiny as part of special counsel Robert Mueller’s investigation. The elder Flynn’s legal defense fund is currently focused solely on his expenses, but it was not immediately clear whether the funds might be used to support the younger Flynn’s expenses as well at some point in the future.

Barry Coburn, Flynn Jr.’s attorney, declined to comment.