The political network backed by billionaire industrialist Charles Koch is spending more than $1 million on an ad campaign to boost Wisconsin Gov. Scott Walker (R).

The Wisconsin chapter of Americans for Prosperity announced Friday that it would spend $1.3 million on digital and TV ads hitting Democratic candidate Tony Evers in the coming weeks.

Evers is challenging the two-term incumbent Walker for the governor's mansion.

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The latest ad campaign comes less than a month after AFP's Wisconsin branch dropped $1.8 million on a series of TV and digital ads touting Walker's record on education.

The latest ads go after Evers, the current state schools superintendent, for floating a possible gas tax hike in the state, claiming that the Democrat's policies would "drive up the cost of construction" on road projects.

"Evers is open to gas tax hikes. Even a dollar more per gallon," a narrator says in the spot. "New tolls too. He says everything is on the table."

Walker is considered among the most vulnerable Republican governors up for reelection this year. The Cook Political Report, an election handicapper, currently rates the race as a toss-up.

Evers leads Walker in several recent public polls. The RealClearPolitics polling average currently puts the Democrat ahead by 3.5 points.