Following weeks of mounting pressure from open-government groups and his Democratic rivals to shed more daylight on his campaign’s fundraising, Mayor Pete Buttigieg’s campaign earlier this month finally relented to demands that he release the names of his campaign’s most lucrative bundlers.

But the candidate who built a national profile and a considerable campaign war chest on a strategy of radical access still faces unanswered questions about his fundraising efforts. And after a primetime attack from Sen. Elizabeth Warren during the most recent Democratic presidential debate sparked a days-long “wine cave”-related news cycle, Buttigieg’s opponents are increasingly happy to pose those questions.

“I don’t spend time with millionaires and billionaires—I don’t meet behind closed doors with big-dollar donors,” Warren told Buttigieg at this month’s Democratic presidential debate. “This ought to be an easy step. And here’s the problem: If you can’t stand up and take the steps that are relatively easy, can’t stand up to the wealthy and well-connected when it is relatively easy when you are a candidate, then how can the American people believe you will stand up to the wealthy and well-connected when you are president and it is really hard?”

In the list released by the campaign earlier this month, Buttigieg’s 146 most productive bundlers—those who have raised at least $25,000 for the campaign by gathering contributions from other donors—are all presented as a single group. But Buttigieg’s campaign, like most modern presidential campaigns, ranks its top bundlers in a series of tiers, with a range of benefits accorded to bundlers depending on the amount of cash raised for the campaign.

In May, Politico reported that the campaign’s top bundlers—part of Buttigieg’s “National Investors Circle,” who pledged to raise at least $250,000 during the Democratic presidential primary—receive a range of perks from the campaign, including monthly briefings with senior campaign staff, access to “Speaker Series conversations,” and quarterly briefings with Buttigieg himself.

“We are inclusive and want everyone to be a part of this effort,” states a memo outlining Buttigieg’s bundling program obtained by Politico. According to the memo, the program provides “mentorship and networking opportunities for both experienced and less experienced fundraisers to connect, strategize, and ideate.”

The practice is common among most presidential campaigns. Even President Donald Trump, who in 2016 eschewed traditional fundraising, divides his bundlers into tiers with corresponding benefits: Bundlers who raised $25,000, known as the “Trump Train,” receive a lapel pin and invitations to leadership dinners and retreats; members of the “Builders Club,” who raise more than $100,000, get access to campaign events like the Republican National Convention.

The Buttigieg campaign declined to delineate the specific tiers for campaign bundlers, name which of its bundlers are at which tier, or describe the corresponding perks associated with each bundler level. But the campaign told The Daily Beast that its initial release is part of an effort “to be the most transparent campaign of the cycle.”

“We are proud to be running a campaign that is powered by the support of more than 700,000 donors from across the country and the only promise any donor gets from Pete is that he will use their money to defeat Donald Trump,” Sean Savett, the Buttigieg campaign’s director of rapid response, told The Daily Beast, noting that the campaign’s $25,000 threshold for revealing bundlers is lower than that of past campaigns. “Whether you can give $3 or $300, whether you are a Democrat, independent or Republican, if you are ready to defeat Donald Trump, we welcome you to our campaign.”

“ As top competitors have sworn off high-dollar fundraisers in favor of small-dollar donations, Buttigieg has faced increased calls to make public the identities of donors who might angle for political favors or ambassadorships down the road. ”

Buttigieg’s campaign has become a fundraising machine, due in no small part to an aggressive fundraising schedule at events hosted by titans of the tech, finance, and entertainment industries. Among Buttigieg’s bundlers are Hamilton James, the executive vice chairman of private equity firm Blackstone; Rep. Don Beyer of Virginia, himself a former Obama bundler; hedge fund manager Orin Kramer; and Broadway theater owner and producer Jordan Roth.

There is no legal requirement for campaigns to release any bundler information, though other presidential campaigns, including that of President Barack Obama, have done so in the past. But as top competitors Warren and Sen. Bernie Sanders of Vermont have sworn off high-dollar fundraisers in favor of pursuing a higher number of small-dollar donations, Buttigieg and other fundraiser-friendly candidates have faced increased calls to make public the identities of donors who might angle for political favors or ambassadorships down the road.

“Bundlers frequently raise vast sums of money for candidates, often hundreds of thousands—if not millions—of dollars, to curry favor with those candidates,” a coalition of 16 advocacy groups, including the Campaign Legal Center, the League of Women Voters, and Public Citizen, wrote in an April letter calling on candidates to name their top bundlers. “We call on you now to implement a system to regularly and meaningfully disclose information about your campaign bundlers.”

Facing similar pressure, former Vice President Joe Biden on Friday released his own list of bundlers who have raised more than $25,000, although, like Buttigieg, he did not outline what benefits those donors might receive, or the campaign’s tiers for bundlers.

Buttigieg has faced similar pressure campaigns from Democratic rivals arguing that he has a transparency problem, ranging from his past work for consulting giant McKinsey & Co. to lingering questions about the demotion of South Bend’s black police chief in the first weeks of his mayoralty. In both cases, Buttigieg pointed to legal complications—a famously stringent non-disclosure agreement and federal wiretapping laws, respectively—as preventing him from being fully candid.

But as Warren continues to hit Buttigieg for allegedly “selling access” to his time, Buttigieg is holding the line on the question of fundraising transparency, at least through the election.

“It’s clearly what has to happen, but it’s not going to happen between now and next November,” Buttigieg told the Des Moines Register’s editorial board when asked about campaign finance reform. “We are building the campaign we’re going to need in order to defeat a president who will pull out all of the stops in order to stay in power.”