Presidential candidate Beto O’Rourke raised $6.1 million in his campaign’s first day, according to his campaign, outpacing all of his Democrat rivals with a possibly record-breaking haul. He won’t, however, disclose how many individual donors contributed or what their average donation was.

It shows that the 46-year-old Texan still has remarkable fundraising ability, which he showcased in the failed Senate bid against Ted Cruz last November that made him a national figure. Before O’Rourke, Sen. Bernie Sanders secured the biggest first-day haul among Democrats with $5.9 million, tapping into a loyal group of supporters from 2016.

O’Rourke initially declined to release his first-day fundraising numbers, and his reluctance to share specifics about the donations has invited skepticism from his critics, who say the eye-popping numbers may be due to a reliance on big-pocketed Democratic donors and donor bundlers, who have previously indicated an interest in O’Rourke.

O’Rourke will be forced to reveal more about his fundraising at the end of March when he files a fundraising report that will be made public on April 15. For his part, Sanders has already said he raised an average donation of $27 from 223,000 donors, relying on mostly small individual contributions. Sen. Kamala Harris came in third place with a first-day haul of $1.5 million back in January. Sen. Elizabeth Warren said she raked in about $300,000.

Most other candidates have been hesitant to share their fundraising numbers. Washington Gov. Jay Inslee, former Colorado Gov. John Hickenlooper, and Sen. Amy Klobuchar all said they raised $1 million over the course of 48 hours. The remaining candidates have not released fundraising numbers.

O’Rourke jumped into the crowded field Friday as one of the more-centrist candidates, and his policy ideas are among the most vague. Though he initially supported Medicare for All — which would provide public health care to every American — O’Rourke has backed away from the idea.

“I think that’s one of the ways to ensure that we get to guaranteed, high-quality health care for every single American,” O’Rourke said of Medicare for All over the weekend. “I’m no longer sure that that’s the fastest way to get there.”