Sen. Bernie Sanders (I-Vt.) scored the first laugh of the fifth Democratic presidential debate on Wednesday by dredging up an old line: "I wrote the damn bill."

Sanders first made the quip - a reference to his signature "Medicare for All" legislation - during the second Democratic primary debate in July after one of his rivals, Rep. Tim Ryan (D-Ohio), suggested that the Vermont senator was unaware of what the single-payer health care proposal actually entailed.

Since then, Sanders has capitalized on that phrase, repeating it at times during public appearances and even selling campaign merchandise emblazoned with the slogan.

It resurfaced once again on Wednesday night after Sen. Elizabeth Warren (D-Mass.), Sanders's chief ideological rival in the presidential race, responded to a debate question about Medicare for All.

Once Warren finished her answer, the debate moderators posed a similar question to Sanders.

"Thank you. I wrote the damn bill," Sanders said as the crowd briefly erupted in laughter.