S&P downgraded the US credit rating from AAA to AA+ based on their view that the recent fiscal plan agreed to by Congress and the administration will not stabilize the country's medium-term debt dynamics. The outlook on the long-term rating is negative and S&P could further lower the rating if debt trajectories are higher than currently expected. While the downgrade may lead to higher borrowing costs, its effects are uncertain and the US debt is still considered safe. Secondary impacts through related markets like money market funds and banks' agency debt holdings could be significant.