Cruz has grown his fundraising every quarter, with his dollar figures rising almost in lock-step with his polling and the general momentum of his campaign.

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He took $4.3 million in the first quarter, then $10 million in the second and $12.2 million in the third. And after beginning his campaign with pundits dismissing his chances, Cruz is now leading in Iowa and has surged to second place in national polls behind billionaire Donald Trump.

The Cruz campaign has built a strong base of small-dollar donors, claiming to have received donations from more than 300,000 people.

Cruz's campaign manager Jeff Roe sent these statistics in a memo to the Texan's campaign staff Wednesday afternoon.

In the memo, provided to The Hill, Roe describes a small-dollar fundraising operation that the rest of the Republican field — with the exception of retired neurosurgeon Ben Carson — will struggle to match.

"Over 10,000 of our donors are ‘sustainers’ who committed to contribute on an automatic, monthly basis, and provide enough recurring revenue ($500,000 a month) to fund our entire field operation," Roe writes.

Cruz is the only Republican candidate in the race to be receiving heavy support at both the high-dollar and low-dollar end.

In the mid-year reports, Cruz's super-PACs disclosed nearly $38 million donations, which put him second only to former Florida Gov. Bush in outside support.

But unlike Bush's super-PAC Right to Rise — which has been spending its $103 million rapidly on TV advertising — Cruz's super-PACs have been sitting on their cash.