MADISON, Wis. — Gov. Scott Walker's first attack ad of the Wisconsin gubernatorial race released Wednesday refers to a sex act while accusing Democratic candidate Tony Evers of not doing enough to revoke the license of a teacher who viewed pornographic images on a school computer.

Walker and his Republican allies have said for more than a year that Evers, the state superintendent, didn't do all he could to remove Middleton middle school teacher Andrew Harris from the classroom. It's been a central issue of the tight governor race. Evers argues Walker is just trying to distract from his failure to address problems facing the state in the past eight years.

Evers has consistently said he didn't then have the legal authority to revoke the teacher's license. He later worked with the Legislature to pass a bill, which Walker signed, expanding the circumstances that warrant revocation.

Republican legislative leaders said Wednesday that Evers hadn't been a leader on the proposal, noting that it had no Democratic co-sponsors and Evers did not personally testify for it, although a representative of the education department did.

The Republican-controlled Legislature passed it unanimously.

Evers' campaign manager, Maggie Gau, accused Walker of making "disgusting, dishonest and increasingly desperate attacks" that reveal his desperation as polls show the race is about even.

"The people of Wisconsin know Tony has spent his lifetime doing what is best for our kids," Gau said, adding that Evers "worked with both parties to toughen the law."

School boards in Wisconsin have the authority to fire teachers. The decision to revoke a teacher's license rests with the state education department that Evers runs. The Legislature changed the law in 2011 to allow for license revocation in cases where teachers view pornography in the classroom, even if students were not exposed to it.

The law in place at the time of the Harris case required students to be endangered by the teacher's "immoral conduct" in order to revoke the teaching license. Evers has cited that as the reason why he couldn't revoke Harris's license — because no students viewed the material in question.

The Walker ad quotes from a Middleton-Cross Plains School District report from 2010 that found Harris had suggested to one student that she "brush up on her sex skills because that's all she'll be good at later in life." Wording from the report referring to oral sex is shown on the screen.

The ad also shows stock footage of young women talking, but not their faces, while the narrator says the teacher "commented on the chest sizes of middle school girls."

The school investigation into Harris began in 2009 when the district received a complaint from a female teacher about emails containing nudity, crude jokes and other inappropriate material that Harris was viewing and sending to other school employees.

Harris was fired in 2010, but an arbitrator determined he should have been suspended so that his punishment would be on par with those given to other teachers who looked at explicit materials or emails while at work.

A circuit court judge and state appeals court upheld the arbitrator's ruling and Harris returned to work in 2014 — which the ad notes with a closing line: "The teacher is still in the classroom with young girls."