It could lead to the loss of jobs, primarily, because as the US credit rating goes from AAA to AA which would be the most likely downgrade credit default swaps, or insurance on bonds, would increase for corporate bond issuers.
The risk right now is that bond insurance firms will get downgraded by the major credit agencies, which means the bonds they insure will be worth less.
One of the ways the market measures credit risks is by looking at the spreds of credit default swaps, a default insurance derivatives market that measures the risk of buying foreign bonds as compared to buying a comparable maturity from the US Treasury.