The short answer is: probably not.
Milwaukee does have city buses which run through downtown, but very few connections to the suburbs. Our bus system is here: http://www.ridemcts.com/routes-schedules. Honestly, I'm not really sure how it compares to other cities in the midwest/ great lakes region. There is also a bus that runs between Milwaukee and Madison (Badger Bus) and there is one train route that runs between Milwaukee and Chicago (Amtrack - Hiawatha route). Uber and Lyft are both available in the city, with reasonable rates (generally cheaper than taxis).
If you are within the downtown area, I think it is doable. But the city is quite spread out (especially compared to European cities). So if you aren't lucky enough to live within a couple blocks from a grocery store or a park or restaurants (or whatever you like to do), it is tough without a car. Most american cities are built around owning and driving a car. I have a car and it certainly seems like a necessity here. That being said, if you think you can do without, I'm sure it is possible.