May's most expensive political race on the ad airwaves in May wasn't the closely fought Pennsylvania Senate GOP primary, which featured two wealthy frontrunners who sunk millions into their own campaign.
It wasn't Georgia's high-profile GOP gubernatorial race, which saw former President Trump ante up, either.
The race that drew the most ad spending in May, per ad-tracking firm AdImpact, was Illinois' gubernatorial race, a race where the primary won't be held until June 28.
Republicans spent $19.7 million on ads over the month, with another $10.5 million coming from Democrats.
Why so much money? Because the race has quickly evolved into a battle of the billionaires.
Hedge fund billionaire Ken Griffin has sunk $45 million into getting Aurora Mayor Richard Irvin elected. And shipping billionaire Richard Uihlein cut Republican state Sen. Darren Bailey a $2.5 million check last month and has been helping to fund an outside group boosting him too.
Irvin's campaign spent $11.1 million on ads this month, more than any other group in the race. The Democratic Governors Association, which has been largely attacking Irvin, spent $6.5 million. Bailey's campaign followed with $4.1 million, just edging out Pritzker's $4 million. The Uihlein-boosted "People Who Play by the Rules PAC" spent another $2.7 million and venture capitalist Jesse Sullivan spent $1.5 million.