A super PAC supporting Gov. Jay Inslee (D-WA) has developed a way to share information and strategy with his presidential campaign in a manner that experts say is both novel and right at the end of the legal boundaries for permissible coordination.

The super PAC, Act Now On Climate, is currently running advertisements with subtle, embedded signals that the campaign can mine for critical voter information and use to hone its own social media and advertising strategies. The tactic has drawn the attention of Democratic digital strategists and raised eyebrows among ethics watchdogs. But the campaign hasn’t asked for the help and says it isn’t mining the data.

“The Inslee campaign is growing grassroots momentum behind the only candidate who will put climate change first,” said Jared Leopold, a spokesman for Inslee. “We are not monitoring messaging data from outside groups."

They apparent key to the scheme is Act Now On Climate’s Facebook page, which it’s used to run hundreds of pro-Inslee ads since March. The vast majority of those ads—all but two of them—link directly to the Inslee campaign’s official website, and urge visitors to sign petitions or register their names and email addresses with the campaign.

It’s rare for a super PAC to so directly promote the work product of the campaign itself. But ANOC’s strategy appears to be geared not only towards advertising Inslee himself but also collecting valuable data that can be used by his campaign—all without ever communicating with the candidate or his staff.

Each of the ANOC ads that link to Inslee’s campaign website uses a unique ID number affixed to the end of the web address. To an average Facebook user, it looks like a meaningless string of characters, something like http://JayInslee.com/join?source=FB&subsource=79. But that “subsource” number is significant: it corresponds to a specific Facebook ad (or series of identical ads) run by ANOC. So far, the page has run promoted Facebook posts linking to Inslee’s campaign website with 73 different “subsource” codes, each corresponding to a different ad.

Administrators of any website can easily see the exact links that visitors clicked to get to that website. So Inslee’s digital staff can tally up visits from a specific “subsource” number. Using Facebook’s public database of political ads, it can then see which ANOC ad used that unique identifier, and it can see the the ages, genders, and locations of the people who viewed the ad, giving the campaign plenty of demographic information about who clicked on a particular super PAC ad.

The resulting information could provide valuable insights into messaging strategy. The campaign could see, for instance, how the messaging in one ANOC ad performed relative to another, or how young people or seniors or women or residents of Iowa or New Hampshire responded to a certain ad’s framing. That could be particularly helpful Inslee, who is currently lagging in the large Democratic field and who is unique among candidates for his aggressive focus on climate change, an issue that even committed activists have found difficult to communicate.

ANOC is run by Corey Platt, a former political director at the Democratic Governors Association, which Inslee led during the 2018 election cycle. Inslee is the only 2020 Democratic contender backed by a candidate-specific super PAC who has not publicly disavowed the group.

On Facebook, ANOC’s ad strategies vary widely—from dire, sincere warnings about the impending damage that climate change will cause to lighter and more youth-focused ads incorporating popular memes and pop culture icons.

Those who click on ANOC’s ads and are directed to Inslee’s campaign website are generally prompted to sign up for the campaign’s email list. There’s no guarantee that they will, but their visit to the website can at least indicate to the campaign that ANOC’s ad was compelling enough to prompt a visit. Through a Facebook technology known as the “Pixel,” the campaign can also keep track of the users who visit its website from any given ANOC ad, and retarget those users later with ads of its own. Though it can’t identify the users by name, having ready-made lists of voters, broken down by which ANOC ad appealed to them, might easily give the campaign a leg-up with its own Facebook ad buys.

The arrangement has struck some Democratic operatives as legally problematic, since Inslee is being provided with information about potential donors and supporters without ever having to spend a dollar from his own campaign account.

Facebook users who follow ANOC’s ads to Inslee’s website and sign up for his email list “have a material value to the campaign,” said one Democratic digital strategist. “The campaigns have to build these lists but they have to do it against the backdrop of a budget. Here, a super PAC that can take unlimited donations is doing the heavy lifting.”

But campaign finance experts say it’s more likely that Inslee’s super PAC is walking up to the edge of the law than stepping over it. Super PACs can accept unlimited donations only because they are technically independent of the campaigns they support. They are legally barred from coordinating with or making contributions—financial or in-kind—to campaigns. Were ANOC to have collected voter information and messaging data, and then packaged and given it to the Inslee campaign, it would likely have violated the law. But simply pushing that data in the campaign’s direction remains permissible.

“My pretty strong instinct is that is a novel and slightly boundary pushing approach but probably within the letter of the law,” said Adav Noti, senior director of the Campaign Legal Center. “Even an aggressive regulator would probably find it to be lawful. And, of course, there is no aggressive regulator right now.”