ATLANTA (AP) — Joe Biden’s presidential campaign is plowing $12 million into a six-state ad buy ahead of the March 10 and March 17 primaries, his largest single advertising effort of the 2020 campaign and a demonstration of his resurgent campaign’s new financial footing.

The former vice president is using two television and digital ads, one a spot touting his relationship with President Barack Obama, the other a new counter to rival Bernie Sanders' current ad campaign hammering Biden on his Social Security record.

The purchase, Biden’s first since his commanding South Carolina primary victory and Super Tuesday surge generated an influx of donor support, underscores that both Biden and Sanders now have the wherewithal to fight it out on the airwaves as long as the nominating fight continues.

A new Biden ad, “Always,” defends against Sanders’ characterization that Biden is a threat to Social Security benefits, a contention the Vermont senator has made for months but ratcheted up since Biden climbed past him in the national delegate count after winning 10 out of 14 Super Tuesday states.

“Joe Biden has always been a strong supporter of Social Security. Biden will increase Social Security benefits and protect it for generations to come,” a narrator intones, before turning the matter back on Sanders. “Negative ads will only help Donald Trump. It’s time we bring our party together.”

A Sanders ad airing in upcoming primary states features Senate audio from a 1990s debate on a balanced-budget amendment to the Constitution. Biden, then a Delaware senator, talks of his work on long-term budget deals that could have curbed some entitlement spending.

The second Biden ad, “Service,” features video of Obama awarding Biden the Presidential Medal of Freedom shortly before the pair ended their second terms in national office. “Joe’s candid, honest counsel made me a better president and a better commander in chief,” Obama says in the video, touting Biden’s various roles in his administration. “All of this makes him the finest vice president we have ever seen. The best part is he’s nowhere close to finished.”

Obama has been a shadow throughout the 2020 contest, with Biden invoking their relationship regularly as he campaigns. Other candidates alternated between criticizing part of the Obama record, such as when Julian Castro hammered Biden in an early debate over Obama-era deportations, and embracing Obama, as billionaire Mike Bloomberg did in his ubiquitous television advertising campaign. Biden expressed frustration at both tacks, defending Obama’s record and noting that his old boss was staying out of the primary and not endorsing anyone.

While that may be the case, Obama has crept back in recently. The former president called Biden to congratulate him on his South Carolina victory Feb. 29, a source with knowledge of the conversation confirmed. With neither Obama or Biden disputing that account, some observers read it as the former president tacit nod toward his vice president as the field winnowed. Sources also confirm that Obama has seen the ad using clips from Biden’s White House medal ceremony.

Separately, Biden has in recent weeks reminded voters that Sanders, a democratic socialist well to Obama’s left, once floated the idea of a primary campaign against the president in his 2012 re-election year.

Still, Social Security may promise to be the bigger fight between Biden and Sanders in the coming weeks. Some Sanders aides have for months surfaced various comments and votes from Biden over the years on entitlement spending, without acknowledging that Sanders himself in the 1990s expressed openness to Social Security “adjustments,” a word that some Sanders allies argued Biden and others used as a euphemism for cuts. Then a representative from Vermont, Sanders also praised an overhaul of the popular safety net program that reduced benefits and increased some taxes under President Ronald Reagan, a Republican.

As presidential candidates in 2020, Sanders and Biden each have proposed protecting and expanding Social Security, so it’s not clear whether either candidate will be able to capitalize on the matter. The Biden campaign on social media this week has pushed back at Sanders by noting that Trump and his fellow Republicans are the more realistic threats to Social Security.

Biden told donors via telephone on Friday that he wanted to avoid “a negative bloodbath” with Sanders.

The new advertising effort includes $8 million on television, with the $4 million spread across radio and digital platforms. The ads will appear across Michigan, Missouri and Mississippi ahead of the March 10 primaries, and in Florida, Illinois and Ohio ahead of the March 17 primaries.

Currently, Biden has 664 delegates to Sanders’ 573, according to Associated Press calculations, with some delegates remaining to be allocated from Super Tuesday. More than 900 delegates are at stake the next two weeks; 1,991 are needed for the nomination.