The notices from the FEC don’t necessarily implicate the campaign in illegal activity or suggest that Sanders’s presidential bid is built on financial fraud. The number of questionable donors and the amount of excessive or invalid contributions still represent a small fraction of the more than $200 million Sanders has collected from more than 2.4 million people. And the letters are only the first step in a lengthy process. They contain warnings that Sanders could face enforcement actions if the campaign doesn’t respond and file amended reports documenting that it has given back excessive or illegal contributions. The campaign has responded to each of the FEC’s previous letters and has refunded hundreds of donations; it has not been fined—although because of the lengthy adjudication process, any penalties are usually levied long after elections. As long as Sanders follows that protocol within the required time period, he wouldn’t face punishment. “It’s a challenge for a campaign that builds up to such a size in such a short amount of time, to be able to handle that,” said Bob Biersack, senior fellow at the Center for Responsive Politics. “I’m not sure how you can avoid this. Because if you get money, you have to disclose it.”

The irony is that Sanders is running as the ethically pure candidate, and yet he’s the one who has struggled the most to comply with FEC rules. As anyone who has ever watched a Sanders stump speech can recite from memory, the average donation to his campaign is $27, and his supporters would argue that a candidate who raises $200 million in mostly small donations from average people is demonstrating broad grassroots support and is less likely to be beholden to a handful of wealthy financiers and their pet causes.

Hillary Clinton has waged the more traditional big-money campaign, using experienced “bundlers” who collect large checks from donors they’ve encouraged to “max-out” to the campaign. The system is built for that kind of fund-raising. Veteran bundlers know FEC rules to the letter and can instruct donors how much to give and when. Fewer checks—or online donations—of larger amounts are easier to process and track than a flood of $27 contributions from people who may have little-to-no knowledge of campaign-finance rules. “It’s just a different animal,” said Lisa Gilbert, the director of CongressWatch for Public Citizen and a veteran advocate for campaign-finance reform. Clinton and Sanders have raised almost the same amount of money during the primary race, but Clinton has collected it from half as many people. The FEC hasn’t flagged a single questionable donor out of more than 1.2 million to her campaign.

That hardly absolves Sanders of the blame for his thousands of overeager supporters and his campaign’s difficulty in complying with federal law. “It is not an infrastructure that most campaigns set up because they don’t have to deal with it. But that doesn’t mean it’s not doable,” Gilbert said. “You should be able to do this right. You should be able to comply and track your donations no matter how many you get and from how many people.” While many people appeared to give just a few hundred dollars more than the $2,700 limit, some donors sent thousands more than the law allows. Two people contributed more than $10,000 to the Sanders effort, and the actor Shia Labeouf gave $6,015—more than twice the legal limit. In some cases, contributions of more than $2,700 that were intended for the primary and general elections might have been misclassified for the primary.