Should I take an additional liability insurance when I rent a car in CA, although I am sure in WI?

I get always loss damage waiver / $ 15 per day, but I need the additional responsibility to an additional 14.50 day? I need the car for two weeks and the cost adds up. Thank you in advance.

You do not need it if you already have insurance on your own vehicle. Make sure to save your insurance information during your trip.