Everything I've read suggests that a downgrade from AAA to AA+ or AA would have have little to no effect on interest rates. The only downgrade that really matte

Everything I've read suggests that a downgrade from AAA to AA+ or AA would have have little to no effect on interest rates. The only downgrade that really matters is from "investment grade" to "junk" status because that prevents many institutional investors from buying bonds. Also remember that most large institutional investors do their own investigation and don't necessarily rely on the ratings agencies.