If you’re a voter you may not have made up your mind yet, but advertisers already have. They know an ad during a presidential debate can be worth a lot.

“During the debate, you not only know that you’re going to get audiences, but you know who the audiences are,” said Ronald Goodstein, an associate professor of marketing at Georgetown’s McDonough School of Business.  

“For the Republican debates — they tend to be more wealthy, they tend to be more Republican, more conservative in their point of view,” he said. 

And for Democratic debates, it’s the other way. But no matter what their politics, said Goodstein, a specific audience is worth a lot more to advertisers than a general one. That means networks can charge a premium for advertising during an election-time event.

“These are a series of mini Super Bowls for them,” said David Campanella, executive vice president, director of national television for Horizon Media, an ad-planning-and-buying firm. Most ads for the debates are sold in advance, and often bundled with the network’s harder to sell time slots. “They use the debates to package less desirable inventory and sell it together,” he said.

That means, unlike Donald Trump who says he won’t participate in Thursday’s debate, advertisers are locked in. “Trump’s not being there could hugely negatively affect viewership,” Goodstein said. “I don’t want to pay 400 percent more and not have the eyes I want.”

Republicans, he said, would have tuned in to hear what the candidate has to say. “And,  if I’m on the other side, I want to see him because I hate him,” he said.

Luckily for advertisers, said David Campanella, most ads on national TV come with a guaranteed number of viewers. Kind of like a campaign promise. But unlike in politics — if a network doesn’t deliver to its advertisers — it still has to make good later.