Democratic presidential candidate Joe Biden continued his attack on Sen. Elizabeth Warren at a fundraiser Wednesday afternoon at a law firm representing companies working in video surveillance, the credit card industry, pharmaceutical manufacturing, health care, and real estate.

Sidley Austin, a notorious K Street lobbying powerhouse, has made at least $2.8 million so far this year representing 29 clients, according to financial disclosures. The $2 billion company is the sixth-largest U.S.-based firm in the world. Its clients include Hikvision USA, a subsidiary of a partially state-owned Chinese manufacturer based in Hangzhou and one of the world’s largest suppliers of video surveillance products; Purdue Pharma; Vifor Pharma; Mastercard; and Huawei, among others. The firm’s top lobbying issues include trade, health, and finance. 

Attendees at the Wednesday lunch reception were named a co-host if they helped to raise $10,000, a sponsor for giving $2,800, a friend at $1,000, and a young professional at $500. Per a pool report from Molly Nagle at ABC News, the fundraiser was hosted by Richard Weiner, a partner at Sidley Austin, and Tony Gardner, former U.S. ambassador to the European Union and senior counsel at the firm. Around 120 people were in attendance, including former NATO Ambassador Doug Lute and former Deputy Secretary of State Tony Blinken, a foreign policy adviser for the Biden campaign, per the pool report. The event was one of three high-dollar fundraisers Biden held on Wednesday alone, including one that was attended by more than 50 Obama administration alumni. 

The campaign declined to provide a comment on the record, other than to note that it does not take contributions from lobbyists, foreign nationals, unions, federal government contractors, national banks, or Securities and Exchange Commission-named executives of fossil fuel companies. While Biden entered the race pledging not to take money from lobbyists, he has held numerous fundraisers with lobbyists.

At the Wednesday fundraiser, Biden waded back into a feud with Warren over Medicare for All. Biden’s deputy campaign manager Kate Bedingfield last week described Warren’s plan to pay for Medicare for All as “mathematical gymnastics.” Warren responded Friday that if Biden didn’t like her plan — which is backed by key Obama administration alums — and wanted to continue defending insurance companies, he was “running in the wrong presidential primary.” Biden later on Friday released a Medium post slamming Warren’s comments and applauding House Speaker Nancy Pelosi’s push build on the Affordable Care Act over implementing a single-payer system.

On Wednesday, Biden said the next president needed to be “somebody who, in fact, knows how to reach across the aisle and get things done. Now the people that are running against me tell me I’m naive, one said I should be in the Republican primary, God love her. That’s not the way you get things done, man. You don’t go in and tell people that they disagree there’s something fundamentally wrong with them.”

While Biden continues to lead the polls, he’s trailing both Warren and Sen. Bernie Sanders, I-Vt., in fundraising. Biden’s campaign last quarter reported only about $9 million of cash on hand — far less than his other Democratic opponents — and has been highlighting the struggle in fundraising emails. During the Wednesday event, Gardner told audience members they had to beat President Donald Trump and the GOP’s latest $125 million fundraising haul. The former vice president’s supporters say he needs to keep up the high-dollar fundraisers if he wants a shot at the nomination.

The fact that Biden hasn’t been able to keep his promises on the campaign finance front underscores one of his biggest challenges: Despite claiming that 98 percent of his campaign’s contributions last quarter were donations under $200, he just can’t seem to harness the energy of grassroots organizers and small donors that has propelled the campaigns of his challengers. Sanders and Warren, meanwhile, have significant grassroots energy behind them, claiming that their campaigns are “100 percent grassroots-funded, and that most of their support comes from contributions of $200 or less.” Both progressive candidates, who’ve sworn off money from corporations and lobbyists, have, however, received contributions from individual employees of lobbying firms, including Sidley Austin. 

Biden continues to be portrayed as the Democratic frontrunner, despite a series of blunders in public appearances and continuously hedging on his various campaign finance pledges. Earlier this month, Biden’s campaign appeared to reverse its pledge to reject money from Super PACs, welcoming a move by several of his prominent supporters to establish a political action committee, Bloomberg reported.