Did the downgrade increase interest rates on U.S. Treasuries 50-basis points? ... Here's FRED data on Treasury 10 years:... They are down a little over 1 full percentage point, from 2.58 percent to 1.51 percent. If you want to consider the baseline the 3 percent interest rates from right before the downgrade, or the 2 percent interest rates that happened afterwards, then rates are down either 1.5 or 0.5 percentage points. That's a major decline in the borrowing cost of the United States. One can't find the increase in rates in this market. Counterfactuals are difficult - perhaps S&P is correct, and 10-year Treasuries would be closer to 1 percent had there been no downgrade.

But that seems unlikely. ... A year later the downgrade appeared to have been irrelevant to United States' borrowing costs. To the extent that they were relevant they signaled and reinforced a further move away from potential stimulus for the economy, which collapsed demand and drove even more money into government bonds and the interest rate down to 2 percent almost right away. But either way, low interest rates on US debt continues their downward march. Contrary to S&P, the financial markets are calling for a larger deficit, not a smaller one.