In a matter of a few hours on Tuesday evening, former Vice President Joe Biden released a digital video advertisement accusing Sen. Bernie Sanders (I-Vt.), a Democratic presidential rival, of lying about Biden’s support for Social Security cuts, and Sanders shot back with a video using Biden’s own words from 1995 indicating support for benefit cuts.

The exchange has given Biden a chance to assure voters that he plans to increase Social Security benefits rather than cut them, despite his record of support for benefit cuts.

But it also puts Sanders in the kind of head-to-head brawl over Social Security he had been craving, and heartens his supporters who worried that rival Democrats were taking advantage of his deference to civility norms.

Biden began the evening with a one-minute video that simultaneously sought to dispel Sanders’ claims that Biden had historically supported Social Security benefit cuts and paint Sanders as a divisive figure willing to “launch dishonest attacks against fellow Democrats.”

In the spot, Biden focused on debunking a very narrow element of the criticism of his record: That in an April 2018 speech at the Brookings Institution in Washington, Biden had backed then-House Speaker Paul Ryan’s vision for Social Security. The ad cited a New York Times column by economist Paul Krugman arguing that Sanders had “flat-out lied” about what Biden said.

And it featured footage of Biden in a vice-presidential debate with Ryan in 2012 explicitly renouncing Social Security privatization, which Ryan had, at one time, championed while serving in the House.

I've been fighting to protect — and expand — Social Security for my whole career. Any suggestion otherwise is just flat-out wrong. pic.twitter.com/KWIIJgFqGk — Joe Biden (Text Join to 30330) (@JoeBiden) January 22, 2020

“Joe Biden has repeatedly voted to save Social Security,” the narrator of the ad says as Biden shakes a man’s hand. “He and President Obama beat back attempts to privatize it.”

Less than two hours later, Sanders answered with a 30-second video quoting from a floor speech Biden delivered in 1995 emphasizing that his vote for the narrowly defeated, constitutional amendment requiring a balanced budget would have applied to Social Security. (By subjecting Social Security to automatic, across-the-board caps absent offsets, such an amendment would have risked cutting the benefits issued by the self-funded program.)

“When I argued if we should freeze federal spending, I meant Social Security as well,” the ad quotes Biden as saying. “I meant Medicare and Medicaid. I meant veterans’ benefits. I meant every single, solitary thing in the government.”

The ad concluded with footage of Sanders declaring at a rally: “We are not gonna cut Social Security ― we are going to expand benefits.”

Let’s be honest, Joe. One of us fought for decades to cut Social Security, and one of us didn’t. But don’t take it from me. Take it from you. pic.twitter.com/qh7qb1Hmcl — Bernie Sanders (@BernieSanders) January 22, 2020

The Sanders campaign also issued a statement from campaign manager Faiz Shakir accusing Biden of initiating a round of negative campaigning.

“Joe Biden just released the first negative ad of the 2020 Democratic primary, and let’s be clear about why: he’s trying to distort his decades-long record of proposing and voting for cuts to Social Security benefits for millions of people,” Shakir said. “Joe Biden is no defender of Social Security, and a negative ad won’t help him outrun his record.”

A Biden official responded by disputing the idea that the video is an ad, let alone a “negative ad.”

“In what world is a social media video with no money behind it, released to defend the Vice President’s record from a slew of attacks, an attack ad?” the official asked.

The Sanders campaign had been trying to lure Biden into a one-on-one slugfest over Social Security for weeks, telegraphing as much ahead of the debate in Des Moines, Iowa, last Wednesday, only to come up empty-handed when the moderators declined to bring it up.

Sanders finally got his chance again on Saturday, when Biden addressed the charges directly to a voter in Iowa.

In Biden’s remarks then and in the ad Tuesday night though, he was able to hone in on an unforced error by the Sanders campaign. PolitiFact correctly noted that a Sanders campaign newsletter did not provide adequate context for Biden’s remarks to Brookings.

Biden took the occasion to clarify that he does not support benefit cuts of any kind. He refers voters to his campaign’s plan to increase benefits for the most vulnerable populations, such as widows and those who have been receiving benefits for two decades or more.

But as Tuesday evening’s clash affirmed, Biden, an avatar of the business-friendly “New Democrats” in the 1980s and ’90s, has a long history of flirting with, endorsing ― and at times actively pushing for ― benefit cuts.

Biden was proud of his vote for the constitutional amendment balancing the budget, which the liberal Center on Budget and Policy Priorities said would have jeopardized Social Security and Medicare, for years afterward.

In a March 1998 press release, Biden boasted that his vote for the constitutional amendment is part of what had earned him the distinction of being rated by National Journal one of the five most conservative Democrats in the Senate. One of his colleagues in the top five grouping was Connecticut Sen. Joe Lieberman, who would go on to endorse Republican Sen. John McCain (Ariz.) in the 2008 presidential election.

It is telling that, in the video, Biden chose to focus on his history of opposing Social Security privatization, a policy pushed by then-President George W. Bush in 2005 that helped hand Congress to the Democrats. Support for the idea is now limited to only the most libertarian corners of the Republican Party; Donald Trump ran in 2016 on a platform of holding the program harmless from any cuts at all.

Rather than embrace privatization, Biden, like other Democrats in the post-Reagan era seeking to upend the stereotype of the “tax-and-spend liberal,” held onto the idea that entertaining Social Security and Medicare cuts was a mark of fiscal seriousness.

Asked in an interview on NBC’s “Meet the Press” in 2007 whether he would consider reducing Social Security and Medicare benefits, Biden confirmed that he would. “You’ve got to put all of it on the table,” he said.

One of the challenges for Sanders is finding a way to make an issue of the most recent elements of Biden’s record without being seen as attacking former President Barack Obama in the process.

Although Obama enjoys sky-high popularity among Democratic voters, Biden’s service in the Obama administration is the most challenging period to reconcile with his present views on Social Security.

Rather than beat back a Social Security privatization scheme as Biden asserts in the video, Obama convened the bipartisan Bowles-Simpson Commission in 2010, which recommended massive cuts to the program. (Incidentally, Bruce Reed, who ran the commission, is now a senior policy adviser for Biden.)

Obama subsequently sought, in budget talks with congressional Republicans to whom Biden served as a liaison, to adopt a “chained” consumer price index that would have effectively reduced Social Security’s cost-of-living adjustment, or COLA.

Obama even included the COLA cut in his budget resolution in April 2013, which is typically seen as a moral wishlist and starting point in negotiations with Congress. The budget was a bridge too far for progressive activists and lawmakers, who rallied outside the White House to protest. Bernie Sanders was one of the featured speakers.