What happens to leftover campaign funds when a candidate drops out of the presidential race?

So far, 23 candidates—both Democratic and Republican—have dropped out of the 2020 presidential race. Some, like Sen. Kamala Harris (D-Calif.) and entrepreneur Andrew Yang, raised north of $30 million. More obscure hopefuls, like former Illinois congressman Joe Walsh, didn’t crack $500,000.

But no matter the scale of their fundraising, each candidate is bound by the rules of the Federal Election Commission (FEC) when it comes to spending their leftover campaign funds.

How candidates can’t spend leftover money

When it comes to personal expenses, candidates can’t (legally) spend a penny they earned from the campaign trail.

As Mental Floss notes, this stems from the fact that, for more than a decade, U.S. representatives who took office prior to January 8, 1980, were allowed to pocket leftover campaign cash after retirement. This led to a fiasco where a third of Congress spent donations from failed campaigns on frivolous items and services, leading to this provision being knocked down.

Today, according to the FEC’s website, their jurisdiction covers the subjects of funds raised and spent to influence federal elections, restrictions on contributions and expenditures made to influence federal elections, and the public financing of presidential campaigns.

If the FEC believes that election law is being violated, they can audit campaign committees, review a complaint, have another government agency refer the violation to them, or have a person or entity self-submit themselves if they believe they committed an error.

How candidates can spend leftover money

If a candidate has dropped out, they can simply refund the money to their donors. They can also donate it to political allies, political parties, or (with a $2,000 limit) other candidates.

They can save leftover campaign funds for a future run, and if cash is needed to bring their failed campaign to a close, they can spend it on that, as well.

Also, there are possible exceptions to the “personal use” prohibition, which Myles Martin, public affairs specialist at the FEC, tells Fortune are handled on a “case-by-case basis.”

“The Commission recognizes that certain expenses made by a campaign may present questions as to whether they constitute bona fide campaign activity or would exist irrespective of the candidate’s campaign or duties as a federal officeholder,” he says.

“Accordingly, the Commission will determine… whether certain uses of funds in a campaign account are permissible, including legal expenses, meal expenses, travel expenses, and vehicle expenses.”

For example, when former New Jersey governor accumulated legal fees during the Bridgegate scandal, he was granted permission to use some of his reelection campaign funds to cover them.

Super PACs complicate things

Some candidates raise funds via Super PACs, political committees that may not contribute to campaigns but can accept donations of unlimited size. They’ve only been around since 2010, when the landmark Citizens United v. Federal Election Commission case paved the way for borderless independent expenditures for political communications by corporations.

As of last month, the second- and third-biggest Super PAC donors are Michael Bloomberg and Tom Steyer, both still in the race.

Beyond not being allowed to fund another federal candidate, Super PACs’ financially borderless nature—and relative newness in the field—means a relative lack of regulation comparative to a regular PAC, which, per year, is limited to contributing $5,000 to a candidate, $15,000 to a political party, and $5,000 to another PAC.

“Super PACs have fairly broad discretion on what they can do with excess funds,” Robert Kelner, chair of the Election and Political Law Practice Group at the law firm Covington & Burling told The New York Times in 2015.

And, he said, the point of any Super PAC is to spend all the money anyway: “Where you see a lot of money left over in the super PAC after the candidate drops out, that will probably tell you something about how seriously the super PAC took the race, to begin with.”

The roots of the FEC

Although its roots date back to President Theodore Roosevelt’s efforts to reform campaign finance law, the FEC was founded partly in response to the financial abuses in the 1972 presidential campaign between George McGovern and incumbent Richard Nixon.

In short, the Campaign for the Re-Election of the President garnered millions of dollars from illegal campaign donors, who were kept on a hidden list by secretary Rose Mary Woods (also made famous for the 18-and-a-half minutes of missing Watergate audio).

After lawyer and campaign finance reformist Fred Wertheimer levied a lawsuit on behalf of the watchdog group Common Cause, the list, which the New York Times called “Rose Mary’s Baby,” was forced into the public.

This resulted in William Keeler, the chief executive of Phillips Petroleum, pleading guilty during post-Watergate prosecutions. In 1974, amendments were made to the Federal Election Campaign Act to set limits on contributions by individuals.

Those amendments included the formation of the FEC to hold those accountable who would send or receive illegal contributions.

In conclusion…

Yang, Harris, former New York City Mayor Bill de Blasio, and the rest legally have their hands tied in terms of what they can do with their millions in campaign contributions.

The Rep. Eric Swalwell (D-Calif.) campaign tells Fortune that after paying all outstanding bills, the remaining balance of Swalwell for America’s funds were transferred to Swalwell for Congress. The other 22 candidates’ committees did not immediately respond to Fortune‘s request for comment.

If they choose to not fund their party, political allies, charities or (to a very small limit) other candidates, they’ll have to wait until 2024 for that money to move an inch.