Darth is right. The original transaction is a valid transaction. Once you broadcast it, you have no way of knowing who has a copy of it.

When you broadcast a new one, like a RBF or just a simple double spend, you are hoping that your new transaction will get mined before the old one does.

But you don't have any way of reaching into other nodes' mempools and deleting the old transaction. So you can never truly cancel it until the new transaction is mined and it makes the old one invalid.