Downgrading USA treasury bonds

Downgrading USA treasury builds doesn't make sense since all financial models have t-bills as safest investment.

For example, if treasuires are downgraded, triple A rated debt would still have higher yield so what's the point.

 

Theoretically, it can affect all debt that is priced "with respect" to treasuries. There will be a parallel shift of yields. :eek:

 

If Moody's downgrades US treasuries, Moody's will become irrelevant.