I did ask this question to TreasuryDirect, but received no answer.
Most weeks the U.S. Government issues Treasury bond products, for terms as short as four weeks. You receive the face value but pay less than the face value. The price is determined though auctions.
You can bid competitively (I will lend you $998 if you pay me $1000 in a month) or non-competitively (I want $1000 in a month and I will pay you whatever the prevailing rate is, which will always be lower than the face value).
The auction happens several days before the bonds are actually issued.
The Treasury has confirmed to me that if one doesn't have the money in the account linked to the website, one simply does not receive the bonds.
The bids, however, have already affected the prevailing price.
What happens when some patriot, wanting to improve the terms on which the Government borrows money, bids billions of dollars in both non-competitive and low price competitive orders, lowering the margin for everyone else?