Some of the presidential candidates at the Democratic primary debate Tuesday questioned “Medicare For All” — but Sen. Bernie Sanders wasn’t having it, saying he knows it’ll benefit workers because, “I wrote the damn bill!”

The Vermont lawmaker was asked if he can guarantee to union members that his health insurance plan would be better than their current health care and responded that he could.

“They will be better because ‘Medicare For All’ is comprehensive, it covers all health care needs,” Sanders said. “For senior citizens, it will finally include dental care, hearing aids and eyeglasses.”

But Rep. Tim Ryan (D-OH) challenged Sanders, chiming in with: “But you don’t know that, Bernie.”

“I do know! I wrote the damn bill!” Sanders snapped.

Former Maryland congressman John Delaney also disputed that the bill was a good idea, arguing it was political suicide.

“You’re wrong,” Sanders said, to laughs.

Delaney argued Democrats shouldn’t be telling Americans their private health care will be made “illegal” because “we don’t want to be the party of subtraction.”

Massachusetts Sen. Elizabeth Warren, who co-sponsored Sanders’ bill, jumped to his defense, arguing that the candidates shouldn’t be using “Republican talking points” against each other.

Delaney pointed out he had experience in the health care business, having co-founded Health Care Financial Partners in 1993, a company that gives loans to smaller health care providers.

“With all do respect I don’t think my colleagues understand the business,” Delaney said.

“It’s not a business!” Sanders said.