From the TSA web site regarding
Secure FLight:
In the near future, small differences between the passenger's ID and the passenger's reservation information, such as the use of a middle initial instead of a full middle name or no middle name/initial at all, will not be an issue for passengers. Over time, passengers should strive to obtain consistency between the name on their government issued ID and the travel information they use for booking flights.
Also, you certainly would not be denied entry. At worst you would be required to have extra screening. You don't even need an ID to get past TSA. If you loose your ID on the way to the airport, they will simply SSSS you. At many airports, it is faster to be SSSS'd than to go through regular screening.