(Yahoo!) -- Former Sen. Jim DeMint (R – S.C.) is standing by the controversial Heritage Foundation study that put a $6.3 trillion price tag on the Senate immigration bill, saying: “There’s no doubt that these numbers are real.”

He also says he has no regrets about leaving the Senate to become president of the Heritage Foundation, recalling his recent years in the Senate as similar to “being on a treadmill going nowhere.”

“I’m at a place now at Heritage where I can have more impact on public policy than I could as a United States senator,” says DeMint.

As the Senate debates an immigration bill, DeMint is at the center of a dispute at Heritage. The conservative policy group released a report last week citing the $6.3 billion cost of the bill over 50 years, which many on both sides of the aisle have rebuked as overblown. The report faced further scrutiny after it was discovered that its co-author, Jason Richwine, has previously made controversial arguments based on race.

While Richwine has since resigned from the Heritage Foundation, and the organization hasdistanced itself from his previous writings, DeMint is not backing away from the report’s findings.

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