The $26.5 million Sen. Ted Cruz's campaign has raised since its inception is due in part to Cruz's most prolific fundraiser: his wife Heidi, who is on leave from her job as a managing director at Goldman Sachs.

Heidi Cruz told The Washington Post last month that she made 600 donor calls in the second quarter, and pores over spreadsheets and donor lists -- and not just the campaign's.

"The calls that I’m making are to max out donors. Max out and super PAC," she said.

Ted Cruz's campaign said Thursday that her calls are not to raise money for the super PAC. Rather, according to spokesman Rick Tyler, the campaign has swapped donor lists with the super PAC and Heidi Cruz is calling donors from both lists, asking them to donate to the campaign. The super PAC and the campaign exchanged donor lists, which Tyler said is legal under FEC rules and said is not a contribution.

A set of narrowly drawn FEC rules approved in 2010 prohibits a campaign from coordinating with an independent group on a paid communication. The agency laid out specific tests to determine whether a campaign has illegally shared internal strategy used to guide an independent group’s advertising.

But the rules do not ban coordination in general, much less conversations between each side. Operatives on both sides can talk to one another directly, as long as they do not discuss candidate strategy. And although a campaign cannot share private strategy with a super PAC, a super PAC can give a campaign information about its plans, as long the group is not sharing something of value that could be considered a contribution.

The FEC also has given candidates its blessing to appear at super PAC fundraisers, as long as they do not solicit more than $5,000 — a decision that came in response to a query from two Democratic super PACs in 2011.

Heidi Cruz spends most of her days on the phone. She told The Washington Post she aims to make 30 each day, but typically does about 20 to 25.

"If you’re having real conversations, it's hard to do more than, like, 25 or 30," she said. "It’s like 10 hours and you take a break here and there. I talk to people for, like, 45 minutes sometimes, it’s, like, a long conversation."