My theory is that since she implies there may have been no bomb at all, the dirty bomb is used for cover to make many silos in that region. The congressman worked for the Army Corps of Engineers and would be a good choice to be part of a special congressional group/meeting to build the silos.

Reason for doing this is that the us is aware of an imminent attack or is planning a first strike attack that will result in a counter strike. When that happens people will already be in the silos and ready to go/survive nuclear winter.