Schimel, the only Republican in a race that also includes three Democrats, said he's taken on plenty of tough cases in his current role as Waukesha County district attorney. He said he wouldn't shy away from doing so as attorney general.
"My oath is to the Constitution, the laws of the state and citizens, and I have to enforce the law without regard to person or place," he said. "So ultimately, unless there was a direct conflict that I had in the case, I would take it."
Schimel said he was speaking hypothetically about the secret investigation, and that he had no inside information about the case. He said he, like everyone else, didn't know whether there was any basis for potential charges.
Milwaukee prosecutors launched two so-called John Doe probes regarding Walker. John Doe investigations are secret probes similar to the federal grand jury process.
The first, which focused on Walker's staff while he was Milwaukee County executive, resulted in no charges against him. The second, which is ongoing, reportedly involves Walker's campaign and conservative groups.
Attorney General J.B. Van Hollen declined to assist in either John Doe investigation. He cited a potential conflict of interest and a possible perception of bias, according to court records filed by prosecutors last week.
Von Hollen, who like Walker is a Republican, is not seeking re-election.
Schimel on Wednesday also announced a plan to help address a backlog in the testing of blood samples for drunken-driving offenses. He said he wanted to shift testing responsibility from the Wisconsin State Laboratory of Hygiene, which also tests food and soil samples, to the State Crime Laboratory, whose sole responsibility is criminal analysis.
Schimel acknowledged that the move would increase the burden on workers in the state crime lab. He said he expected it would require a shift of resources from the Hygiene Lab.
A message left with the Hygiene Lab was not immediately returned.
Schimel's remarks came during a panel discussion with reporters at the Milwaukee Press Club. He answered questions about a number of topics, including his own arrest in 1990 for drunken driving. He said he and a friend had left a Milwaukee concert and he thought he was OK to drive, but when a police officer pulled him over and asked him to step out of the car he realized he wasn't.
"I am contrite about that, I do regret it, I do take responsibility for it," he said. "I have spent the last 24 years trying to pay back the community for that by making my community safer."
The three panelists also named a number of controversial state laws and asked whether he would decline to defend any of them. Those he pledged to defend included the ban on same-sex marriages; a law that requires abortion doctors to have admitting privileges at nearby hospitals; and a voter idnetification bill that's on hold pending court challenges. In each case, he said he wasn't aware of any legal precedent ruling that the laws were unconstitutional.
"It won't be my job to decide which laws I think are good and bad," he said. "It'll be my job to assess which laws pass the constitutional test."
The three Democratic candidates in the attorney general race are district attorneys Ismael Ozanne in Dane County and Susan Happ in Jefferson County, and state Rep. Jon Richards. Schimel would face the winner of the Democratic primary.
Associated Press writer M.L. Johnson contributed to this report.