WASHINGTON ― Sen. Bernie Sanders (I-Vt.) is demanding that President-elect Donald Trump immediately promise to veto any legislation that would cut Social Security, Medicare or Medicaid.

“Right now, before Congress wastes an enormous amount of time, Donald Trump has got to come forward ― maybe through a tweet, one of his tweets ― and say clearly that Donald Trump will veto any legislation that cuts Medicare, that cuts Medicaid or that cuts Social Security,” the former presidential candidate said Wednesday at a press conference following a meeting between Democratic congressional leadership and President Barack Obama.

“And if he makes that clear to his Republican colleagues, we can save us all a whole lot of time and start getting to work doing what this country desperately needs to have done,” he added.

Trump must make this clear because he campaigned on promises not to cut the three social insurance programs, Sanders argued, specifically referencing a May 2015 tweet in which the then-prospective candidate touted his early public opposition to benefit cuts.

I was the first & only potential GOP candidate to state there will be no cuts to Social Security, Medicare & Medicaid. Huckabee copied me. — Donald J. Trump (@realDonaldTrump) May 7, 2015

”Trump didn’t just say this in passing. He didn’t say it in the middle of the night. He didn’t say it in a particular interview,” Sanders said. “This was a cornerstone of his campaign. He said it over and over and over again.”

Sanders later blew up the tweet as a visual aid for a similar speech on the Senate floor.

Bernie just printed out a gigantic Trump tweet and brought it to the Senate floor https://t.co/kl9QbohqGO pic.twitter.com/nNrq4JlZZT — Gizmodo (@Gizmodo) January 4, 2017

If Trump fails to promise to veto any cuts to three programs, Sanders said it would be clear the president-elect had “simply lied to the elderly and the working people of this country and just made campaign promises that he had no intention of ever keeping.”

In fact, Trump routinely promised to protect Social Security and Medicare ― universal programs that middle-class seniors rely on ― from cuts, but referenced the means-tested Medicaid far less frequently.

Still, Sanders clearly views Trump’s campaign-trail attempts to fashion himself a defender of the elderly as a source of political vulnerability for the president-elect.

Republicans may be happy to let bygones be bygones now that Trump has handed them control of the White House, but Sanders is not letting him off the hook so easily. At a press conference about opposing Medicare cuts in early December, he pressured Trump using a similar promise to “hold [him] accountable” for his campaign promises.

Last week, Sanders also warned Trump against trying to privatize the Department of Veterans Affairs, a view that is shared by major veterans groups like the American Legion. As chair of the Senate Committee on Veterans Affairs in 2014, Sanders presided over a bipartisan reform package that drew praise from Republican colleagues.

The Trump transition team did not respond to a request for comment about Sanders’ challenge.

This article has been updated to include Sanders’ floor speech on Wednesday.