Super PACs must operate independently of candidates, and their donors are eventually disclosed, though that disclosure will come long after Nevada holds its caucuses on Saturday.

At the last Democratic debate, in New Hampshire, Ms. Warren had used the fact that neither she nor Senator Amy Klobuchar of Minnesota had a super PAC as a cudgel to hit the rest of their opponents. “Everyone on this stage except Amy and me is either a billionaire or is receiving help from PACs that can do unlimited spending,” she said then.

On Tuesday, a super PAC supportive of Ms. Klobuchar, which calls itself the Kitchen Table Conversations PAC, also began reserving more than $400,000 in television time in Nevada and South Carolina. The first ad focuses on Ms. Klobuchar’s advocacy for women who have been kicked out of hospitals after giving birth.

The Klobuchar campaign stood by its opposition to super PACs while not explicitly calling for the new group to pull its ads.

With the two new super PACs, every candidate who will be on the debate stage in Las Vegas on Wednesday is either a billionaire (former Mayor Michael R. Bloomberg of New York) or supported by super PACs that are not subject to campaign contribution limits (former Vice President Joseph R. Biden Jr., former Mayor Pete Buttigieg of South Bend, Ind., and Senator Bernie Sanders of Vermont). Tom Steyer, another billionaire, is competing aggressively in Nevada but did not qualify for this debate.