If you don't have (sufficient) liability insurance (from your own car insurance at home), then you need buy liability insurance for that rental. You may be able buy it from the car rental company (but check in advance if that's what you want to do!), or you may able to find a third-party source. But it is not included in the standard "primary insurance" of any "normal" credit card including Chase United.

"Primary" vs "secondary" refers to who kicks in first (not to what's covered). If you have an injury-free collision, "primary" means the card kicks in first and you may not need to notify your own insurance company at all, while "secondary" means your insurance company covers it first, and then the credit card only covers deductibles/etc (anything your insurance company didn't pay).

But rental car insurance on most credit cards is collision (or collision+theft) coverage only.