With Donald Trump’s campaign sinking in the polls, there has been on and off speculation that he’s got his eye on creating some kind of conservative media company after the election.

Those rumors were fanned again recently with a report that his son-in-law was already in talks about implementing such a move. Speculation had also been stirred by Trump’s hiring of Steve Bannon, founder of ultra-conservative news site Breitbart, for his campaign.

But another clue to Trump’s intentions can be found a bit more under the radar, according to Dave Helmreich, chief operating officer of LiveIntent. The company partners with about 1,300 publishers to place ads at the beginning of their email newsletters.

Now before you start yawning (email? newsletters?), consider that these partners include the New York Times and Wall Street Journal, and the email newsletters reach about 140 million people in the U.S. That means LiveIntent’s ad network reaches more folks than Twitter or Snapchat. Basically, LiveIntent helps marketers and advertisers place their message into these email newsletters using various targeting tools.

A large portion of these email newsletter ads work as some kind of call to action (“Click here if you want to help make America great again!”). Someone clicks on the ad, and they are taken to a website where they are asked to do something (donate, sign a petition, etc.). And often, doing that something involves entering your email address. The result: Email newsletter ads are an extremely effective way to rapidly build a huge email list for a third party who has purchased that ad.

As it turns out, one of LiveIntent’s most successful customers these days is the campaign of Donald J. Trump. Now, the Hillary Clinton campaign is also a customer. But Trump’s investment and impact have been far greater. And that means Trump is building a monster email list of people who are eager to hear his message.

“We’ve seen him spend an inordinate amount of time and energy on our platform,” Helmreich said. “We’re seeing two times the number of emails being captured from right-leaning groups compared to the left.”

If nothing else, Trump will be left with an incredibly valuable asset when this is all done. In politics, candidates frequently sell or rent their lists to other marketers or candidates. There are often few restrictions on how they can use the emails they’ve amassed.

But even so, email is becoming increasingly important to media companies, according to Helmreich. It gives them a valuable way to reach a targeted audience without having to rely on the whims of platforms like Facebook and Twitter or on Google searches. Helmreich pointed to a number of companies — including Vox, BuzzFeed, and the aforementioned Breitbart — that have used their email newsletters to launch and grow media businesses.

So, why not Trump?

Helmreich said the email newsletters have been especially effective for Trump because they tend to reach an older, wealthier demographic.

Indeed, throughout this year, Trump and PACs supporting him have consistently outperformed Clinton and her PACs, according to LiveIntent’s data. Back in March, 54 percent more people were clicking through right-leaning email newsletter ads than left-leaning ones. By August, that gap had grown to 246 percent more for Trump PACs, as compared to Clinton PACs.

Turning to the first debate, which was widely considered a catastrophe for Trump by the mainstream media, we can see that his supporters were in fact quite energized by it.

According to LiveIntent, on they day before the first debate, 400 percent more people were clicking through ads for Trump and related PACs than for Clinton-friendly groups. During the debate, that jumped to 740 percent, and after the debate it jumped to 913 percent.

Though not every single click results in a captured email address, we can assume most do. For Trump, that’s a lot of email addresses from people who have clearly indicated that they like what they hear from him and want more. With just over two weeks left before the election, these are people who are also still donating money to his troubled campaign, turning out in large numbers for rallies, and following him on Twitter.

And in some ways, Trump seems to be already leveraging his base of emails and his social media following. He sent out an email last night inviting his supporters to watch a debate program featuring analysts of his choosing appearing on a Facebook Live stream that got more than 8 million views.

We’ll have to wait until after November 8 to learn whether Trump really has any media empire ambitions. But even this week, in an interview with CNN, Bannon didn’t do much to stomp down conjecture.

When a CNN reporter asked about the media empire speculation, Bannon just said: “Trump is an entrepreneur.”