MANCHESTER, New Hampshire – A lavish Martha’s Vineyard Democratic fundraiser that Bernie Sanders attended in 2007 featured lobbyists for many of the industries he now rails against on the presidential campaign trail, according to a guest list obtained by MSNBC.

The Vermont senator’s appearance at the event underscores the challenge Sanders faces in trying to address criticism that he has both not done enough to help fellow Democrats and that he’s fallen short of the very high bar for campaign finance purity he’s set for himself. Helping Democrats often means collecting checks from wealthy donors and industry executives, whom he has made the enemy of the “political revolution” he hopes to spark.

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The core message of Sanders’ presidential campaign is that the political system and the economy is rigged by corporate interests who essentially bribe politicians to do their bidding through campaign donations. By relying on small contributions from regular donors to fund his campaigns, Sanders argues he has not fallen prey to the special interests that infect most others in public life, including Hillary Clinton.

Clinton has argued that by that standard, everyone would fail. “I’ve heard Senator Sanders’ comments, and it’s really caused me to wonder who’s left in the progressive wing of the Democratic Party,” Clinton said in Thursday’s MSNBC debate in New Hampshire. “Under his definition, President Obama is not progressive because he took donations from Wall Street.”

The Democratic Senatorial Campaign Committee (DSCC) holds a fundraiser on the tony Massachusetts island of Martha’s Vineyard every summer, which Sanders has attended several times to help raise funds for the campaign arm of Senate Democrats. Sanders is an independent who caucuses with the party.

Previously unreported are details about who exactly attended those fundraisers. A guest list shared with MSNBC from the 2007 event – the first year Sanders was in the Senate – shows the fundraiser featured 20 Democratic senators and their spouses, along with more than 100 lobbyists and wealthy donors who had donated the then-maximum $28,500 to the DSCC.

A Sanders campaign aide said the senator attended these events reluctantly and noted that New York Sen. Chuck Schumer, who has warmer relations with Wall Street, was leading the DSCC at the time and that Sanders and Schumer don’t agree on everything.

“The people who financially support the Democratic Party need to hear the message that Bernie is delivering and that is resonating all over the country. It is also important that the Democrats take back the Senate,” said spokesperson Michael Briggs.

The 2007 Martha’s Vineyard fundraiser guest list included professional lobbyists, corporate executives, trade association heads, labor union brass and wealthy individual donors.

Some are government relations executives directly employed by corporations such as the financial firms Blackrock and Prudential Financial, or the defense contractor Raytheon. Others represent large Washington law and lobbying firms, such as DLA Piper, Patton Boggs, and Akin Gump.

Some names stand out, like John Breaux, the former Democratic senator from Louisiana turned mega-lobbyist who has worked for Citigroup, Goldman Sachs, Wal-Mart, Chevron, ExxonMobil and more. Then there’s former Texas Lieutenant Governor Ben Barnes, who has represented many petrochemical and pipeline companies as well as Stanford Financial, the now defunct financial firm felled by an alleged Ponzi scheme.

Other guests included a lobbyist for the private equity firm Blackstone Group as well as those who have represented pipeline company Kinder Morgan, the American Petroleum Institute, pharmaceutical giants such as Merck and Allergan (now involved in a controversial inversion deal), and the pharmaceutical trade association, among others.

It’s not clear whether Sanders interacted directly with these people at the relatively large event. The invitation list also included some labor union executives, liberal donors and representatives of progressive causes, like the Civil Liberties List. And it included some close friends and allies of the Clintons, like Elizabeth Bagley, whom Bill Clinton appointed ambassador to Portugal.

Sanders has funded his presidential campaign largely through small online donations, but funding Democratic senatorial campaigns might be a challenge if as president he barred large donors like those present at the Martha’s Vineyard event.