It’s almost as if they’re worried.

Correct the Record, a super PAC whose mission is supposedly to respond to attacks against Hillary Clinton, instead turned its focus on Bernie Sanders yesterday. In an email sent to the Huffington Post, the super PAC tied Sanders the British Labour Party’s new leader, Jeremy Corbyn, and Hugo Chavez, who provided discounted fuel to Vermont in a deal Sanders supported.

As they wrote:

The email, sent to a Huffington Post reporter in response to an article about Corbyn and Sanders without any agreement that it would be off the record, was meant to flag Corbyn’s “most extreme comments.” Among those was the suggestion that the assassination of Osama bin Laden was “a tragedy,” since there was no attempt to arrest the former al Qaeda leader and put him on trial. The email also cites Corbyn’s comment that he’d invite his “friends” from Hezbollah to come to the U.K. to discuss peace in the Middle East and an editorial in which he said that the North Atlantic Treaty Organization’s “attempt to encircle Russia is one of the big threats of our time.” … The more serious stretch comes as the email highlights how Sanders helped negotiate a program with Venezuela’s national oil company in 2006 that provided discounted heating oil assistance to low-income Vermonters. The senator said it was “not a partisan issue,” in the state, which was the sixth to make the deal. His support for the program was apparently enough to merit a mention, since Corbyn has written that the late Venezuelan leader Hugo Chavez’s “electoral democratic credentials are beyond reproach.”

For their part, Hillary Clinton’s campaign has itself said it would not be attacking Sanders, who has made a point to avoid attacking her when prompted to do so.

But Correct the Record is undoubtedly part of Clinton’s network of campaign organizations, even if they aren’t part of her official campaign. And the fact that they felt the need to get a dig in on Sanders shows that her network is starting to worry about Sanders’s marked rise in the polls of late:

In response, the Sanders campaign pointed out to the Post that, for all of their talk about correcting the record, the super PAC’s charge is a stretch at best, writing in an email that, “To equate bringing home heating oil to low-income Vermonters with support for the Chavez government is dishonest.”

It’s also dishonest to directly tie Sanders to Corbyn. While they are both running against the establishment from the left in their respective countries’ liberal parties, and Sanders did say that he was “delighted” that Corbyn’s bid for Labour’s leadership was successful, that’s where their similarities end. All those things Corbyn said about bin Laden, Hezbollah and Russia? There is precisely zero reason to believe Sanders agrees. It would make about as much sense to imply that Hillary Clinton is for overturning Roe v Wade because she and Rick Santorum are both members of The Family — a charge that Correct the Record would be positively apoplectic over.

It’s also notable that Correct the Record’s note wasn’t circulated to the public directly, but was instead sent to reporters. And given the substance of the attack — referencing old issues and foreign leaders — it’s unlikely that it was intended for direct public consumption (How many Democratic primary voters have strong thoughts and feelings about Jeremy Corbyn?). Correct the Record didn’t want the public to know that this information from Sanders was coming from them, they wanted it to seep into the next articles that major media outlets write about him.

If Bernie Sanders is starting to take hits from the Clinton camp, that can only be taken as a good sign for him. It means that Clinton’s allies are starting to take him seriously as a threat. For now, the attacks are only coming through surrogates and in emails to reporters, but it’s likely a sign of more direct, and public, shots to come.