Do you legally have to have car insurance?

If I remember correctly, most if not all states require some form of insurance. In most cases only liability is required to satisfy the minimum financial responsibility requirement for a state. The consequences of driving without insurance can be severe. In some states if you are pulled over or have an accident (at fault or not), you can have your license suspensed/revoked, your vehicle registration suspended (you wouldn't be able to renew your tags), among other possible punishments.