The Democratic candidate, Jodi Habush Sinykin, a lawyer who is unopposed in her primary, is running television ads aimed at raising Ms. Brandtjen’s profile.
A parade of women in Ms. Habush Sinykin’s ads call Ms. Brandtjen “too conservative” and cite her opposition to abortion rights and her citation as “pro-life legislator of the year” from a Wisconsin organization that opposes abortion rights.
In all, Ms. Habush Sinykin has spent $166,000 on advertising, while neither Ms. Brandtjen nor Mr. Knodl has bought any television or digital ads, according to AdImpact, a media-tracking firm.
Ms. Habush Sinykin declined a request to be interviewed about the campaign and her advertisements. Democratic polling of the race suggests that she could beat Ms. Brandtjen in a general election but would have a far tougher race against Mr. Knodl.
“We’re continuing to highlight Janel Brandtjen and how she would be a disaster in the State Senate,” said Joe Oslund, a spokesman for the Democratic Party of Wisconsin. “We’re going to continue to put her extremism front and center for voters.”
Wisconsin Republicans hold a 21-11 advantage in the State Senate after the state adopted new G.O.P.-drawn legislative maps ahead of the midterm elections. If a Republican wins the special election to the Senate, the party will hold a veto-proof majority and will have the votes to impeach Gov. Tony Evers, a Democrat, his appointees to state cabinet posts and state judges.
Like many once solidly Republican suburban areas, the district, which covers parts of four counties in Milwaukee’s northern and northwestern suburbs, has trended toward Democrats in recent years. Mr. Trump won the district by 12 percentage points in 2016, but that advantage narrowed to five points in 2020. In 2018, Gov. Scott Walker, a Republican, won the district by 20.5 points, but last year the G.O.P. nominee for governor, Tim Michels, carried it by just four points.
The seat opened up when Alberta Darling, a 78-year-old moderate Republican who was first elected in 1992, announced her retirement in November. Mr. Evers praised her as “a diligent leader who’s always carried herself with poise, class, and grace.”
Kitty Bennett contributed research.
