“The idea that deficits don’t matter for countries that can borrow in their own currency I think is just wrong,” Powell said during congressional testimony in the Senate.

The notion behind what is called “Modern Monetary Theory,” or MMT, is that as long as the Fed can keep interest rates low without sparking inflation, the national debt and budget deficit won’t be an issue. MMT has been espoused by politicians including Rep. Alexandria Ocasio-Cortez, D-N.Y., and Democratic presidential candidate Sen. Bernie Sanders of Vermont.

Powell conceded that he has not read up on the theory but said he has heard some “pretty extreme claims” about how it might be implemented.