Standard & Poor's changed its outlook on the government-sponsored enterprises this week to negative from stable, mirroring its move on U.S. debt obligations earlier. When analysts placed the U.S. sovereign rating on negative outlook, it pointed to the conservatorship of Fannie Mae and Freddie Mac as the main cause. Analysts estimated it could cost 3.5% of GDP to capitalize and relaunch Fannie and Freddie – in addition to the 1% GDP already invested. Analysts affirmed the triple-A rating on the GSEs. The outlook revision pertains to Fannie, Freddie and 10 of the 12 Federal Home Loan Banks, excluding those located in Chicago and Seattle. The credit of the GSEs is "constrained by the long-term sovereign rating on the U.S." And the outlook and rating for the GSEs will change if the U.S. sovereign rating is downgraded, according to S&P. "We derive our opinion of the support included in the ratings based on the links and roles attached to the supporting entity, the U.S. government," analysts said. Jim Vogel of FTN Financial said the S&P move on the GSEs was expected and investors are unlikely to change their strategies. "The segment that limits GSE debt purchases now won't buy any less," Vogel said. "The rest that have been comfortable with GSE investment characteristics are unlikely to buy any less either." S&P said it does not expect to downgrade the U.S. Analysts at Capital Economics, said "we wouldn't be too surprised to see the U.S. lose its triple-A rating, at least temporarily. But there are a number of reasons why U.S. debt will still remain attractive to borrowers." Write to Jon Prior. Follow him on Twitter @JonAPrior.