The Moody’s announcement sent the yield on a 30-year Treasury bond to a high of 5.01% at one point on Monday. Bond yields rise as bond prices fall. When a selloff hits and demand for bonds dries up, it sends bond prices lower. In turn, bond yields move higher.

Moody’s has downgraded the nation’s credit rating one notch to Aa1, leaving the U.S. without a top grade among any of the major rating agencies.