Inside Sen. Bernie Sanders’ presidential campaign there has always been a sense of vulnerability about the attacks that would come against the senator over the wealth he has accumulated in office. After all, it becomes a bit tricky for a politician to rail against the perniciousness of income inequality when he himself becomes a member of the well-off, even if that fortune is simply due to a best-selling book.

But few expected that one of the first jabs would come from one of the most firmly Democratic-allied media outlets in the country.

This week, ThinkProgress, the news organ that is a project of, though editorially independent from, the progressive think tank Center for American Progress, put out a video noting that Sanders had stopped maligning millionaires—choosing, instead, to direct his ire at billionaires—when he became a millionaire himself.

The video accompanied a more nuanced article reflecting on the irony of Sanders dragging his feet in releasing his tax returns out of a desire to hide his wealth while President Trump refused to release tax returns in order to keep secret that he wasn’t as rich as he boasted. And in an email to The Daily Beast, Jodi Enda, the editor of ThinkProgress, defended the work as observational more than adversarial.

“ThinkProgress did not try to ‘go after’ Sen. Sanders—to use your words—and we will not ‘go after’ any other candidate,” Enda said. “We strive to be fair and to allow our readers and viewers to interpret the news for themselves. We are no different from other media in that regard.”

“The video illustrated how Sen. Sanders’ rhetoric has evolved,” Enda added.

A source at the Center for American Progress stressed that no one at the think tank had insight about, or input into, the video that ThinkProgress produced. But within the broader Democratic ecosystem, those editorial lines of demarcation were not exactly satisfying.

The video was viewed as an implicit warning that a portion of the party’s infrastructure would not simply be content to let Sanders coast through the primary (as if that was in doubt). And a number of progressives expressed dismay to The Daily Beast that one of the party’s more notable media arms had chosen to attack Sanders for his wealth well before any of his fellow primary candidates had. It did not go unnoticed that the video was being gleefully passed around by GOP operatives on Twitter.

What made the video all the more remarkable, however, was that Sanders’ campaign manager, Faiz Shakir, was not too long ago the editor of ThinkProgress. Shakir said he had no comment on the matter. But his relationship with the officials at CAP is complicated, after he began providing assistance to Sanders’ 2016 campaign—all of which was revealed during the dumping of stolen emails by Wikieaks during the late stages of that campaign.

But there was an obvious explanation for why that grated on CAP officials. They were largely supportive of Hillary Clinton, from the organizations founder (John Podesta) to its current president (Neera Tanden).

There is no Clinton in the race this go round. But, it appears, the skepticism towards Sanders persists.