CNN  — 

A pro-Martin O’Malley super PAC knocked Bernie Sanders over guns in a short video posted on Thursday, the first time a group associated with the former Maryland governor attacked his foremost progressive opponent in the bid to emerge as Hillary Clinton’s main competition.

The ad by Generation Forward PAC, titled “Time for a Debate,” may be tacit acknowledgment by the O’Malley camp that the former Maryland governor’s poll numbers are stagnating while the senator’s are rising.

After noting that Sanders voted against the Brady Bill and voted to give gun manufacturers protections against lawsuits, the ad bluntly says, “Bernie Sanders is no progressive when it comes to guns.”

At a press conference on Capitol Hill Thursday, Sanders declined to directly address the ad, stating instead that “if you look at my record, you will find that we do have a strong record” on guns.

The latest chapter in the gun control debate was sparked after a white man walked into a historically black church in Charleston, South Carolina, last week and killed nine African-Americans in a racially-motivated attack.

In the eyes of gun control activists, Sanders has a mixed and moderate background on the issue, something that contrasts with his more liberal persona. For much of his career, Sanders has followed the lead of his Vermont constituents – who mostly back gun rights for hunters – by keeping a generally states’ rights view of gun laws.

But Sanders has voted to tighten gun laws in the past. He approved the 1994 assault weapons ban, and after the shootings in Newtown, Connecticut in 2012, Sanders backed Obama’s failed push for more background checks and another assault weapons ban.

Last week, Sanders took a cautious approach when CNN questioned him about his position on gun laws, stating that he thinks “we need to have a conversation about” laws, but that rural and urban America need to understand how each other feel before laws move forward.

After a follow-up question, Sanders shied away from the debate. “I will talk about guns at some length, but not right now,” he said, a comment that contrasted with his usual blunt, brash and proudly liberal persona.

Unlike Sanders, O’Malley has consistently backed tighter gun control laws. His team regularly claims that he passed the “most comprehensive gun control law in the country” in 2013, a law that banned new assault weapons, lowered magazine capacity, required fingerprints for firearm purchase and increased regulations on gun dealers.

After the shooting in Charleston, O’Malley told his supporters via email that he was “pissed” about the nation’s unwillingness to pass gun control.

Recent polling has shown O’Malley is falling behind while Sanders is surging. Both declared their presidential bids earlier this year, running to be the liberal alternative to Clinton, the race’s frontrunner.

A Fox News poll out Wednesday found that O’Malley gets 1% of national Democratic support, compared to Sanders who enjoyed 15%. Clinton is way out in front, however, with 61% support.

O’Malley is equally behind in early states, according to a Bloomberg Politics poll. The former Maryland governor has 2% support, according to the poll, in both Iowa and New Hampshire. Sanders has 24% in both early voting states.