Legal Question in Real Estate Law in California

Can it be? Probably yes; depends upon what the lease says is the purpose of the deposit. Must it he? No. It would be the landlord's option in most cases. Rarely if ever does the landlord HAVE to apply the deposit to past-due rent. This is because the deposit ordinarily must be maintained at the fill 100% level throughout the lease term unless the landlord waives the requirement. A deposit is not the same as the last month's rent. However, leases are not all the same, so read yours and see what it says about maintaining the deposit, use of the deposit as rent, etc.