Depending on which town you are in, the level of enforcement is different in different counties, Wisconsin has some of the best laws for tenants in the country. With that being said-it depends on what your goal really is. If you are looking just get out or do you want the "quiet enjoyment" of the unit you are in. I will assume that you are looking to stay.
First, write a letter to the landlord explaining the conditions.Give him/her a time limit to fix the issue. Send the letter return receipt requested. The post office can show you what I mean. Second, the second after the time limit expires, contact the local housing officials, health department, and city inspectors. They can and will force the landlord to fix or remedy any health or safety issues. Contact them by phone and later by letter. If this does not solve the problem. Then it is time to contact the lawyers. They can tell you how to withhold rent or the procedures you need to follow to terminate the lease.
Best of luck,
I did a little research it turns out Wisconsin does have provisions for tenant rights. Please see http://datcp.wi.gov/uploads/Consumer/pdf/TenantsRights143.pdf . Also you can call the Wisconsin Toll Free number at (800) 422-7128. I highly recommend speaking to someone in your state's agency and remember to write down the name and date of the person you speak with.
Best of luck.