It seems a fitting way to welcome Pete Buttigieg to the top tier of 2020 Democratic presidential candidates. Two major Democratic power players ― Steve Elmendorf and Barry Karas ― would host a fundraiser for the South Bend, Indiana, mayor, the first openly gay man to seek the presidency, collecting checks worth up to $5,600 to add to his already healthy campaign coffers.

But the event, which was first reported by NBC News, also highlights a potentially awkward fact: Buttigieg, a Rhodes scholar and military veteran, is the only high-level contender who would take money from Elmendorf, a former top aide to Richard Gephardt, who was House Democratic leader from 1989 to 2003, and one of the city’s most powerful lobbyists.

Of the top tier of active candidates seeking the 2020 Democratic presidential nomination ― usually identified by pundits to include Sen. Bernie Sanders (I-Vt.), Sen. Kamala Harris (D-Calif.), Buttigieg, former Rep. Beto O’Rourke (D-Texas), Sen. Elizabeth Warren (D-Mass.) and Sen. Cory Booker (D-N.J.) ― only Buttigieg is actively accepting donations from Washington lobbyists. Several lower-profile candidates, including former Colorado Gov. John Hickenlooper and Washington Gov. Jay Inslee, are also taking lobbyist cash.

It’s unclear whether former Vice President Joe Biden, a leading potential candidate who is expected to enter the presidential race soon, will take lobbyist money. A Biden spokesman didn’t respond to an email seeking comment.

Progressive groups have pushed Democratic candidates to swear off both lobbyist money and support from super PACs during the primary process, arguing the party’s past reliance on the rich for campaign funds has skewed policymaking and prevented Democrats from adequately challenging moneyed interests and economic inequality.

“Too many voters believe that both parties are funded by the same special interests,” said Adam Green, the co-founder of the Progressive Campaign Change Committee, which has endorsed Warren. “If Democrats want to inspire voters to get off the sidelines so we can defeat Trump, then now is the time to purify our brand and do things like reject corporate PAC donations and money from corporate lobbyists.”

Washington lobbyists have donated to some of the other candidates in the top tier, but candidates have promised to return that money. The Federal Election Commission reports from both Booker and Harris, for instance, show cases where they returned donations from lobbyists.

During a Friday town hall in Somersworth, New Hampshire, a voter sharply questioned O’Rourke about a donation he received from a Chevron lobbyist, saying the donation “made it harder for us to believe” O’Rourke’s campaign promises to fight climate change.

“I was just told as we drove in that we accepted on one of the last days of the FEC filing period a check from a lobbyist. We are returning that check from the lobbyist,” O’Rourke responded.