President Donald Trump’s new budget chief thinks Social Security is a scam. But some progressive members of Congress aren’t giving up the fight to save it.

On Friday, Sen. Bernie Sanders (I-Vt.) and Rep. Peter DeFazio (D-Ore.) introduced a bill to make Social Security solvent for generations while also expanding benefits.

The bill would lift the payroll tax cap on highest earners and extend the life of the program through 2078. Currently, Social Security is funded through a 6.2% payroll tax that only applies to the first $127,200 a person earns in a year. The Sanders plan is similar to one he proposed during his presidential campaign and would lift the cap on all income above $250,000.

Sanders proposed his legislation on Thursday because it was Social Security Day of Action. That's the day of the year — not even two months in — that millionaires stop contributing money from their paychecks into Social Security because of the $127,200 cap.

Trump vowed on the campaign trail not to make any cuts to Social Security, but members of his cabinet may have other plans. Mick Mulvaney, Trump's recently confirmed head of the Office of Management and Budget, refused to walk back his position that Social Security a "Ponzi scheme," during his confirmation hearings.

"I wouldn't read too much into the description of it as a Ponzi scheme," he told senators during his confirmation hearing. "It’s simply describing to people how the cash flows." When pressed by Sanders about whether he would try and keep Trump's promise not to cut benefits, Mulvaney suggested raising the retirement age — which would cut years of Social Security benefits for retirees.

In addition to lifting the payroll tax cap for top earners, the Sanders-DeFazio plan also expands benefits to retirees by changing metrics used to calculate benefits, including the cost of living adjustment.