Vukmir began her day at the North Shore GOP field office in Milwaukee.
"This is exciting, and it's part of a final-week push of 32 cities and 30 counties," Vukmir said.
Vukmir urged her supporters to get out to the polls on Tuesday. She's been endorsed by the Republican Party of Wisconsin.
"We need to send a proven, consistent conservative to Washington to join President Donald Trump," Vukmir said.
Vukmir had a total of six campaign stops scheduled on Monday, including a rally with House Speaker Paul Ryan in Racine County.
Nicholson spent part of his afternoon on Monday knocking on doors in Pewaukee. He said he'll be doing a lot of door-knocking and phone-banking in the final hours of the campaign.
"My promise to Republican primary voters is, 'Give me your vote, and I'm going to deliver the future of this country for you," Nicholson said.
Nicholson said he's working to energize supporters ahead of tomorrow's primary election.
"It's going to take an outsider with real-world experience," Nicholson said. "Mine's in the U.S. Marines, but also in business, and in my time as a husband and a father. That's what's going to allow me to get things done."
Mordecai Lee, a professor of political science at UW-Milwaukee and former Democratic state lawmakers, said he expects turnout to be high for Tuesday's primary because of the Nicholson-Vukmir primary as well as the primary election to nominate the Democratic candidate for Governor.
Eight Democrats are vying for the chance to challenge incumbent Republican Scott Walker in November.
"I'm guessing we're going to see an unprecedented, high turnout," Lee said.
He expects more than one million votes to be cast tomorrow, which would be a turnout of more than 20 percent of eligible voters.
Lee expects loyal Republicans to vote in the Senate primary, and loyal Democrats to vote in the primary for Governor.
But he said which race independents decide to vote in, because they can't vote in both, could decide who moves on to November's general election.
"I think some primary voters will be frustrated because they want to vote in both races," Lee said.
"To a certain extent, this is the excitement of democracy," Lee said. "Because what's going to happen tomorrow night at 8 p.m., no one has the vaguest idea."