Did Facebook’s ad platform give Donald Trump an unfair advantage in the 2016 election? That’s a question I tried to answer last October, when I looked at how the dynamics of the ad platform can promote more polarizing ads. It came up again over the weekend, as more people digested Antonio García Martínez’s op-ed in Wired, which examines the same issue. Here’s how he put it:

During the run-up to the election, the Trump and Clinton campaigns bid ruthlessly for the same online real estate in front of the same swing-state voters. But because Trump used provocative content to stoke social media buzz, and he was better able to drive likes, comments, and shares than Clinton, his bids received a boost from Facebook’s click model, effectively winning him more media for less money. In essence, Clinton was paying Manhattan prices for the square footage on your smartphone’s screen, while Trump was paying Detroit prices. Facebook users in swing states who felt Trump had taken over their news feeds may not have been hallucinating.

The question is how big that discrepancy really is. I have some new information to share here, but first we need to review how CPMs work on Facebook. From my October story:

To place an ad on Facebook, a political campaign has to win an automated auction. At any given time, millions of advertisers are competing to place ads in front of Facebook’s 2 billion-plus daily users. Advertisers can price their ads by the number of people who see it, the number of people who click on a link, or the number of people who engage with the ad, such as by watching a video or installing an app. Facebook averages out the cost of these various ads into a figure it calls an “eCPM” — the effective cost per 1,000 impressions. The CPM is a standard measurement in the advertising industry. But Facebook’s ads differ from traditional ads in an important way: the company offers advertisers a monetary incentive to create more engaging ads. As users begin to click, share, and engage with an ad, Facebook begins showing it to more people. That lowers the eCPM, often allowing advertisers to reach a larger audience for the same amount of money. In some cases, Facebook’s automated systems will choose to display ads that had lower bids, if it believes the content of the ad will draw more engagement from users. The monetary goal of this system is to keep users scrolling through the News Feed, maximizing the number of ads that they encounter.

In my piece, I wrote about a senior Facebook employee who said Trump’s CPM was substantially lower than Clinton’s, according to communications I reviewed. At the time, I couldn’t find a second source for something else the employee said, which was that Trump’s effective CPM averaged $0.06, compared with $1.06 for Clinton.

Then came a tweet over the weekend from Brad Parscale, who led Trump’s digital advertising efforts. Parscale hadn’t responded when I asked him for comment last year, but he was happy to boast to Wired editor Nicholas Thompson: “I bet we were 100x to 200x her. We had CPMs that were pennies in some cases. This is why @realDonaldTrump was a perfect candidate for FaceBook.” (No, I don’t know why he capitalized the B. #EditTweets)

So how much did the Clinton campaign pay? Here it gets a bit tricky. Last fall, a member of the Clinton campaign team told me that their CPMs averaged $10 to $30, which they described as typical for a targeted Facebook campaign. But that figure represented the cost only of paid impressions. As described above, ads that perform well can reach larger audiences as they receive likes, comments, and shares — so-called “organic reach.” That lowers the overall cost of the ad.

When Parscale says “we had CPMs that were pennies in some cases,” he almost certainly took organic reach into account. (It’s very hard to place an ad for anything on Facebook for literal pennies.) Unfortunately, the person I spoke with at the Clinton campaign no longer had access to organic reach data. Still, they said, it was unlikely that organic reach would have lowered a $10 paid CPM to a $1 organic one, as my Facebook source had suggested.

Facebook’s official word to me on the subject last year was that no candidate had a clear advantage in CPMs. More polarizing messages can be more expensive to distribute precisely because they reflect minority viewpoints, the spokesman said. If people see something they disagree with, they’re more likely to click away from Facebook — making the ad more expensive.

But whatever the exact difference in CPM may have been, it’s clear the Trump campaign benefited from the dynamics of the platform. It reached more people for less money, and it appears that the difference in reach was substantial.

Andrew Bosworth, who ran Facebook’s ad platform during the 2016 election, tweeted today that the platform is now less susceptible to being gamed than it once was. But there’s mounting evidence that during the campaign, polarizing messages did resonate broadly. And for Donald Trump, they resonated quite cheaply.