I heard one of the rating agencies have considered downgrading US Treasuries from AAA to AA.
This sounds like an urban legend. The dollar starts dropping, and some people start claiming that the sky is falling.
The rating of a bond or related investment is really based on the expected chances of it being paid back.
There is nearly a 100% chance of the US Treasuries being paid back. Why? It is impossible for the U.S. government to go bankrupt. Why? They can just print more dollar bills.
That's not to say that bad things can't happen -- printing too many dollars can cause inflation, or even hyper-inflation. But if the U.S. government doesn't pay money that it owes, the consequences are much more far-reaching than losing money from an investment.
The relative *value* of a US Treasury may be going down, if the dollar containues to slide. But if you lower US Treasuries from AAA to AA, then you have to lower all other bonds issued in the U.S. to a maximum of AA.