"This is the heart of Trump country," said Vukmir, who was campaigning in the area on Tuesday with U.S. Rep. Sean Duffy, R-Wausau. "This is the part of the state, central Wisconsin and northern, that came through for him and advocates for him."

Trump won Wisconsin by less than 1 percentage point, but he carried the county where he's appearing Wednesday 56 percent to 38 percent. He won the mostly rural congressional district by 21 points — the widest margin of any congressional district in the state.

Getting out the GOP base in areas that went big for Trump will be important for both Vukmir and Walker. Polls show the race between Walker and Democratic challenger Tony Evers, the state schools superintendent, is a tossup. Baldwin, who is running for a second term, has consistently led Vukmir, a state senator, in fundraising and in polls.

Walker on Tuesday released a new television ad attacking Evers over his support for in-state tuition for children of people living in the U.S. illegally and of issuing driver's licenses to immigrants here illegally. The spot ends with the line: "Tony Evers: special treatment for illegals, higher taxes for you."

Evers decried the ad as a desperate move to mimic Trump, who has been using campaign rallies to increase his anti-immigrant rhetoric.