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There's a small hitch in Jeb Bush's plan to rely on massive super PAC money.

The “vast majority” of TV ads backing Bush are paid for by his super PAC, which has to pay as much as 1,000 percent more for the ads than his campaign would, Politico reports. So while Bush and allies will be spending $5 million more on ads in the first four voting states than rival Marco Rubio and his allies, there will be more Rubio ads on air. On broadcast TV alone, Rubio will have 5,000 more ads.

Federal law limits how much TV stations can charge campaigns, but that doesn’t apply to super PACs. “Who’s going to go weeping for the super PAC that gets gouged?” Elizabeth Wilner of Kantar Media told Fortune in September. 

An early lesson from this election is that super PACs might not be quite as powerful as anticipated. They alone can’t sustain a campaign. Scott Walker had to drop out of the race despite a well-funded super PAC, because, as The New York Times noted, those groups “cannot pay rent, phone bills, salaries, airfares or ballot access fees.”