Not a very clear explanation. You could have just copy and pasted this though, as it explains your point:
A purchase order (PO) is a commercial document issued by a buyer to a seller, indicating types, quantities, and agreed prices for products or services the seller will provide to the buyer. Sending a purchase order to a supplier constitutes a legal offer to buy products or services. Acceptance of a purchase order by a seller usually forms a contract between the buyer and seller, so no contract exists until the purchase order is accepted. It is used to control the purchasing of products and services from external suppliers.
The key is that no contract exists until both parties have agreed to the purchase order.
A purchase order shows intent and constitutes an offer, but it is not a binding contract in an of itself.
The real questions should be, "Why is DHS needing 1.6 billion rounds of ammunition that is not allowed to be used in war? And how is that not wasteful spending in our current economic situation.? Shouldn't that funding be put toward healthcare, welfare, and social security, as well as education?"