A key architect of California’s controversial billionaire tax acknowledged this week that the proposed one-time levy may end up becoming permanent.

Economics professor Emmanuel Saez made made the admission during a Tuesday debate against Arthur Laffer , the father of trickle-down economics, at the University of California, Berkeley.

Attendees cheer during the speach of US Senator Bernie Sanders, Independent of Vermont, during the campaign kickoff for the California Billionaire Tax Act. AFP via Getty Images

The billionaires tax — proposed by the Service Employees International Union–United Healthcare Workers West — would impose a one-time 5% levy on California residents with assets exceeding $1 billion.

Supporters say the tax is needed to address healthcare funding gaps tied to cuts to Medicaid and other federal programs implemented last year.

The proposal has yet to formally get on the ballot in November for voters to decide on it, but supporters recently announced that they had the required number of…