Rental of what?
But whatever it is your question is irrelevant. Whether mandatory or not whoever is renting whatever to you requires that you insure it against loss or damage, and that's their right as a condition of rental.
So if it's car rental and you're in a state where car insurance is not mandatory all car rental providers can and will insist uponninsurance cover. You buy theirs or you buy elsewhere and show proof to them that it has at least equal coverage to the cover they offered you.
Rental insurance for what? A home? An automobile? What.
To whatever you are referring the insurance policy can be offered by any licensed insurance provider, not just Nationwide.
mandatory probably not but if you're talking about renters insurance on a apartment your renting not a bad idea for an average of about 99 bucks a year
Rental insurance for what? And no, it doesn't have to be Nationwide. Any registered insurer will do.