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 downgrade of the U.S. credit rating made it the third of the three major ratings agencies to downgrade U.S. credit since 2011 amid widening budget deficits.