“I have stopped raising money for him until I see the campaign correct its problems,” Crane said. “I wasn’t going to raise money to spend on a futile crusade.”

Overall, the pro-Paul super-PACs have seen only a tiny fraction of cash held by the Kentucky senator's Republican opponents.

Texas Sen. Ted Cruz exceeds Paul's super-PAC haul by more than $20 million, and even both candidates who have already quit the race - Wisconsin Gov. Scott Walker and former Texas Gov. Rick Perry - outraised Paul on the super-PAC side.

Reporting only $1.15 million by June 30, Purple PAC has about a third of the money held by the largest super-PAC supporting Paul. In its mid-year FEC accounts, the top pro-Paul group - America's Liberty PAC - reported $3.1 million in contributions.