A campaign spending group affiliated with the left-wing Justice Democrats has released a new video ad taking aim at former Vice President Joe Biden’s past support for Social Security cuts.

The group, Organize for Justice, announced earlier this month that it plans to spend $500,000 on digital ads attacking Biden and former South Bend, Indiana, Mayor Pete Buttigieg ― the two moderate front-runners in the race for the Democratic presidential nomination ― in the early states of Iowa, New Hampshire and South Carolina.

The initial round of ads promoted unflattering stories about the candidates on Facebook and other digital venues. But on Wednesday, amid an escalating battle between Biden and Sen. Bernie Sanders (I-Vt.) over Social Security, the group unveiled a 30-second video spot about Biden’s Social Security and Medicare record.

“Only the most heartless Republican would go after these vital protections,” the video’s narrator says.

The ad then shows footage of Senate Majority Leader Mitch McConnell (R-Ky.), President Donald Trump and then-Delaware Sen. Joe Biden discussing cuts to social programs. The clip of Biden is excerpted from a speech Biden delivered on the Senate floor in 1995 touting his vote for a constitutional amendment to balance the budget in which he underscores that his vote would have frozen federal spending on Social Security, Medicare and Medicaid. (It’s the same speech that Sanders used in a video blasting Biden on Tuesday night.)

“Ask Joe Biden: Why did he join Republicans to attack benefits for seniors?” the narrator concludes. 

Biden has said that as president, he would not even consider benefit cuts. Rather, he insists he would increase benefits, pointing to his campaign’s policy plan to boost payments to some of the most vulnerable groups of seniors. And in an appearance on MSNBC’s “Morning Joe” on Wednesday morning, Biden argued that holding him responsible for his past stances on the program is akin to faulting Sanders for votes in the 1990s against gun safety regulations.

But Alexandra Rojas, executive director of Justice Democrats and president of the board of Organize for Justice, insisted that Biden’s record is fair game.

“Biden has never explained why he changed his mind about cutting Social Security,” Rojas said in a statement. “Iowans deserve to know the truth about all the candidates’ records.”

Organize for Justice is structured as a 501(c)4, which means it is able to receive and spend large amounts of money with less frequent disclosure than an ordinary political campaign or political action committee. 

The Buttigieg campaign targeted the group’s lighter disclosure requirements in a campaign fundraising email.

“We just learned there’s a pro-Bernie dark money group running digital ads against Pete in Iowa and New Hampshire,” the campaign email wrote.

Justice Democrats and Organize for Justice were founded by alumni of Sanders’ 2016 run, but neither of the groups has endorsed a candidate in the current Democratic presidential primary.