The U.S. credit rating was downgraded by Moody's Ratings on Friday, highlighting investor concerns about the government's growing debt.The downgrade from the top rating of Aaa to Aa1 "reflects the increase over more than a decade in government debt and interest payment ratios to levels that are significantly higher than similarly rated sovereigns,

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.