Bernie Sanders and Elizabeth Warren supporters not looking forward to a potential Joe Biden nomination might want to time-travel back to 1972.

That year, Biden was an underdog Senate candidate running against a popular incumbent. With his sister, Valerie, as campaign manager and limited resources, he knocked on hundreds of doors and embraced a progressive message centered around ending the Vietnam war, protecting the environment and supporting civil rights. He directed particular ire at millionaires who didn’t pay taxes and mega-corporations that grew rich while being subsidized by the public.

The Democrats’ exceptionally leftwing 1972 platform called for an expansion of key entitlement programs and, as the journalist Branko Marcetic writes in Yesterday’s Man: The Case Against Joe Biden, the prospective senator was fully onboard. The call for automatic cost-of-living increases for social security recipients figured prominently in the 29-year-old’s stump speech. As Biden told a crowd of Delaware autoworkers, the program needed to be more generous, “raised to a level where people can live in dignity”. They rewarded him with a United Autoworkers Union endorsement, support that would be crucial in his narrow victory.

A decade later, the “New Deal Democrat” had completely changed his tune. As the Reagan era dawned, Biden recalls listening to friends “mostly on the Republican side of the aisle”. “More and more,” he became “a believer in balanced budgets.”

By 1984, Biden took his newfound small-government approach to its logical conclusion and proposed a total federal spending freeze. A majority of states had double-digit unemployment rates at the time, and there were widespread economic worries. But instead of taking aim at the structural reasons for decline, Biden focused single-mindedly on the deficit. Along with two Republican colleagues, he spearheaded a plan to “shock the living devil out of everyone in the US Senate” by freezing spending, including cost-of-living adjustments for social security recipients. This despite a majority of Americans supporting more funding for the program, even if it meant higher taxes. At the time, inflation was nearing 5%, so effectively Biden would have taken billions of dollars away from working people.

“Middle-class Joe” from Scranton, Pennsylvania, the economic populist of 1972, was long gone. And he never regretted his shift. In 1995, when he finally had a Republican majority to work with in the Senate, Biden reminded his colleagues that “When I argued that we should freeze federal spending, I meant social security as well, I meant Medicare and Medicaid.” He joined only a handful of Democrats in backing a Republican proposal to enshrine small government into the constitution through a balanced budget amendment.

He was just as unremorseful when running for president in 2007, telling Tim Russert on Meet the Press he wasn’t afraid of the “third rail” of American politics – entitlement reform, even cuts to popular programs. In particular, he touted the idea of “protecting” social security by raising the retirement age.

In the early weeks of 2020, this troubling history has finally gotten mainstream attention. It’s been mostly driven by the Sanders campaign, which is eager to cut into Biden’s huge lead among older voters. And it has sparked a lot of back and forth between the Sanders and Biden camps about particular episodes of the former vice-president’s record, and whether or not he’s being misrepresented. But the general arc of Biden’s time in Washington – from campaigning on the expansion of entitlement programs to calling for cuts to them – is undeniable.

Bernie Sanders also ran his first Senate campaign in 1972, on a platform denouncing “the world of Richard Nixon, and the millionaires and billionaires whom he represents”. Like the young Biden, he vigorously defended the threadbare American welfare state. Unlike Biden, he continued that defense throughout his political career.

Today, 62% of retirees draw half or more of their monthly income from social security. Without it, 15 million more people would be in poverty. Medicare is no less vital to the well-being of older Americans.

Biden is certainly not alone in “evolving” his stances on these vital programs. In fact, his career is a perfect case study of how much the Democratic party changed in a generation, as the progressivism of the McGovern campaign morphed into the retreat of the Reagan years and then the triangulation of the Clinton-era.

Democratic politicians may have “evolved”, but Democratic voters, for the large part, haven’t. Most still want robust social programs. And with older Democrats at the core of his 2020 nomination hopes, Biden better hope that they are forgiving.