So far, they have cause for worry. Mr. Burton’s super PAC, Priorities USA Action, and a companion nonprofit group was at the end of February about one-tenth of the way toward its goal of raising $100 million, struggling with inexperience and missteps against more successful super PACs supporting Republican candidates.

Although the Obama re-election campaign has collected about $157 million, more than the four GOP presidential candidates combined, Priorities USA Action is getting trounced by the anti-Obama super PACs, which have raised more than $100 million by the end of February, a number that doesn’t include money going to related nonprofit groups…

Leonard Barrack, founding partner of a law firm based in Philadelphia and for years a mainstay of Democratic fundraising, was unhappy with the overture from the super PAC. He said he first heard from Priorities USA last month in an email from adviser Paul Begala, a former Clinton White House aide. The email invited Mr. Barrack, a former chairman of the Democratic Party’s national finance committee, to click on a link to contribute. He hit delete instead.

“Put me down as not being approached properly,” Mr. Barrack said, adding that an email pitch was no substitute for personal outreach. Asked about the email, Mr. Begala said, “You just reminded me, I need to go up and see him.”