A super PAC run by former aides to Sen. Bernie Sanders (I-Vt.) is preparing to launch its first TV spot boosting presumptive Democratic presidential nominee Joe Biden among progressives who remain reluctant to support the former vice president.

The ad from America’s Progressive Promise PAC is backed by a six-figure cable buy and will run nationally during the Democratic National Convention later this month. It's not clear exactly how much the group plans to spend on the television spot.

The ad highlights Sanders's endorsement of Biden earlier this year, in which he said that the former vice president “would be the most progressive president since” Franklin Delano Roosevelt. 

“Every person who voted for me and for the other candidates understands Donald Trump is the most dangerous president in the history of our country, and that it is absolutely imperative that we come together to defeat him — and defeat him badly,” Sanders says in the ad. 

Former top aides to Sanders’s presidential campaign — including Jeff Weaver, who managed Sanders’s 2016 White House run and served as a senior adviser to his 2020 bid — formed America’s Progressive Promise PAC in late April.

The group, in partnership with Nuestro PAC, a super PAC founded by another former Sanders adviser, Chuck Rocha, is focused on turning out the Vermont senator’s core supporters — among them, Latinos, young voters and progressives — for Biden in the general election. 

That coalition will prove crucial to Biden’s electoral success in November, Weaver said. 

“The importance of the Democratic primary coalition that supported Senator Sanders cannot be overstated in the general election and it is critical that we reach out to them,” he said. “And there is no more effective messenger than Bernie Sanders in his own words.”

There is some evidence that Sanders’s supporters are lining up behind Biden ahead of the general election. Polling from The New York Times and Siena College released in June showed that among battleground state voters who said Sanders was their top choice for president, 87 percent plan to back Biden. 

Sanders proved to be Biden’s most formidable opponent during the Democratic presidential primary contest, racking up a series of early wins in key primary and caucus states like New Hampshire and Nevada before falling behind in the weeks after the South Carolina primary.

The two candidates differed significantly on policy, with Biden representing the moderate wing of the Democratic Party and Sanders leading its ascendent progressive wing. After Sanders suspended his presidential campaign in April, he endorsed Biden and the two engaged in a lengthy unity process in an effort to consolidate Democratic support for the presumptive nominee’s general election bid.

Weaver acknowledged the differences between Sanders and Biden on Friday, but said ousting President Trump in November should remain the top focus for progressives. 

“There are certainly policy differences between Senator Sanders and Vice President Biden, but as Bernie Sanders has made clear, we must all come together to defeat Donald Trump and elect Joe Biden,” Weaver said. "Those of us in the progressive movement will continue to push for transformative change after the election, but there won’t be any progress if Trump is re-elected.”

America’s Progressive Promise PAC isn’t the only progressive group urging Sanders’s supporters to rally behind Biden; RootsAction.org, a group run by Sanders’s backers, launched its #VoteTrumpOut campaign on Wednesday in an effort to turn out progressive voters for Biden in key battleground states.