Here is an interesting little tidbit regarding Debit Card credit these days.
It seems that during the fat times, Chase Bank was automatically tacking onto their Checking/Debit Cards a form of overdraft protection. It was a simple line of credit that crept up over time (ours was $10k per account). If memory serves, there was no credit application, no credit request — it just was an option offered one day many years ago.
It worked as an automatic extension of credit — spend more than was in your account, and you did not bounce a check or get denied on a debit card purchase. You would be charged for an entirely separate line — a whole new account number, different invoicing and statements, etc. And, you could not pay it by depositing money into your checking account — you had to make a specific payment to that credit line.
Now, it seems, that Chase (part of JP Morgan) is becoming a bit tighter with their credit lines. You have to affirmatively request this line in person at a bank branch.
I assume the new credit card laws have something to do with this . . .