The consensus among mortgage market watchers is that the downgrade earlier this month of the GSEs by Standard & Poor’s will have no immediate, detrimental impact even as Fitch Ratings this week said it is keeping Fannie Mae and Freddie Mac’s “AAA” rating.Fitch this week also said its outlook for Fannie and Freddie’s ratings remained “stable.” The move was in concert with Fitch’s decision to keep its rating on U.S. debt at the highest grade.“A key element of the explicit support is the guarantee by the U.S. Treasury to inject funds into Fannie Mae and Freddie Mac, so that each firm can avoid being considered technically insolvent by their regulator,” said the rating agency.