In an election hyper-focused on special interests and their grip on politics, nearly all of the Democratic front-runners for president have pledged to reject campaign donations from lobbyists.

But former Vice President Joe Biden and former South Bend, Indiana, Mayor Pete Buttigieg both raised thousands of dollars from registered federal lobbyists, according to new campaign finance disclosures the candidates were required to file Friday. Donors included lobbyists who have represented the fossil fuel industry, for-profit college companies and major pharmaceutical makers.

Buttigieg raised nearly $6,000, Biden raised nearly $3,000, and Sen. Amy Klobuchar (D-Minn.) raised $500 from individuals who have worked as federal lobbyists within the past year.

Sen. Bernie Sanders raised just over $1,000 in mostly small, recurring donations from registered lobbyists but had not specifically promised not to do so. Warren, who also pledged to eschew lobbyist fundraising, refunded several donations made by federal lobbyists.

The Biden campaign said it would return the donations HuffPost flagged if it had not already done so, and the Buttigieg campaign said it was looking into whether it should refund the money. After publication, the Klobuchar campaign said it would return the donations as well.

Buttigieg in recent days has sent fundraising emails touting his rejection of special interest cash. “At Pete for America, we have kept our promises to voters,” reads a recent example. “We do not accept money from corporate PACs, fossil fuel executives, or lobbyists. But with four days until the Iowa Caucuses, we can’t fall behind on our fundraising efforts.”

But his campaign’s disclosures list 13 individuals who were registered as lobbyists in 2019 and 2018, including Christina Franz, who recently represented the American Chemistry Council, a giant fossil-fuel industry trade group, and Christa Bierma, who lobbied for the National Restaurant Association as Republicans crafted the 2017 tax reform bill.

Biden accepted $1,740 from Gregory Hahn, an Indianapolis attorney whose clients have included an Indiana for-profit college test prep company accused of scamming its customers. His campaign also took donations from a longtime attorney and lobbyist for pharmaceutical manufacturers, Robert Kingham, and lobbyists with numerous ties to the natural gas industry and other pharmaceutical companies. A lobbyist who specializes in advising “major multinationals and high-net-worth individuals on international tax issues,” Philip West, donated $500.

According to the Federal Election Commission disclosures, none of these donations was refunded (which is what campaigns typically mean when they “reject” undesirable donations) before the end of 2019.

The Biden campaign had either refunded the donations HuffPost flagged or was in the process of doing so, a spokesman for the campaign said.

“We are vigilant in screening donations,” Sean Savett, a Buttigieg campaign spokesperson, told HuffPost, “but with more than 730,000 donors, some may slip through, and we want to thank you for bringing these donations to our attention.”

The Sanders campaign did not immediately respond to requests for comment.

All of the Democratic candidates for president have made some promise to reject campaign cash from powerful special interests. Every single candidate pledged to refuse campaign donations from corporate PACs. Most of the remaining front-runners — including Klobuchar, Biden, Buttigieg and Sen. Elizabeth Warren (D-Mass.) — have promised to reject donations from federal lobbyists, and Sanders has promised to reject donations from pharmaceutical lobbyists.

That promise is not as straightforward as it sounds. The common understanding of what counts as lobbying is much broader than what the federal law counts as lobbying. Washington is full of hundreds of people working for issue groups, corporate public relations, trade associations and law firms who don’t have to register as lobbyists even though the bulk of their work involves influencing lawmakers. And for the relative few who are considered lobbyists under federal law, the law is notoriously easy to evade.

Campaigns get to make their own determination about what counts as a lobbyist, and they tend to like the narrower definition. In April, Biden held a fundraiser with the executive who oversees Comcast’s lobbying arm but is not himself a registered lobbyist. And erstwhile candidate Beto O’Rourke accepted donations from the chief executive of a giant lobbying firm called Subject Matter.

Sanders’s campaign, too, accepted roughly $1,000 from two federal lobbyists. The lobbyists who gave to his campaign were Ian Thompson, an American Civil Liberties Union lobbyist who made contributions totaling $735.62, and Marilyn Park, a lobbyist for the American Federation of Government Employees union, who gave a total of $377.70.