Issue credit ratings are based, in varying degrees, on the following considerations:
1.Likelihood of payment--capacity and willingness of the obligor to meet its financial commitment on an obligation in accordance with the terms of the obligation;
2.Nature of and provisions of the obligation;
3.Protection afforded by, and relative position of, the obligation in the event of bankruptcy, reorganization, or other arrangement under the laws of bankruptcy and other laws affecting creditors' rights.

To put it more clearly, a sovereign rating is the result of political and macro-economic data assessment.
As to the way those criteria interact, it takes more than a simple post, perhaps even a diary.

US Government bonds are obviously rated AAA.<s>

What would push the USA sovereign rating down ? this is a good topic for a PhD essay. Who volunteers ? :)

When through hell, just keep going. W. Churchill