In his endorsement message, Mr. Trump blamed Mr. Vos for blocking efforts to conduct a “full cyber forensic audit” of the 2020 election and said he had “refused to do anything to right the wrongs that were done.”

“Speaker Vos had 17 years to prove to Wisconsin residents that he has their best interest in mind, but even in his own campaign efforts, Vos has tried to mislead his constituents, sending out mailers that feature a picture he took with me — trying to make voters believe I am a Vos supporter, which I am not,” Mr. Trump said. “I do not come close to supporting him.”…

Mr. Steen, 38, is running on a platform that echoes the former president’s election grievances. He said that if Mr. Vos, who has been Wisconsin’s Assembly speaker for a decade, were removed from office, new leadership would be more amenable to holding a decertification vote, which Mr. Vos has blocked on grounds that it is impossible to decertify the results of a past election.

“I would have voted to pull back our electors because fraud vitiates everything,” Mr. Steen said in the interview on Monday, using a phrase common on the far right among those seeking to overturn past election results. “When you’re looking at the fact that we have an election that has lots of questions, I’d say, ‘Why, why?’ Could you tell me why Robin doesn’t want to look at it? I don’t know.”