I don't think de-invest is an actual word, but I will role with you on this. Investors treat U.S. Treasury bonds like cash. A lot of financial transactions are actually done with Treasury notes, because they are considered extremely safe and reliable, and unlike cash, they generate interest payments. If investors don't like the downgrade, then they will sell off their bonds for cash. Cash is theoretically the safest asset you can hold (some would argue that gold is, but that is a different topic). Cash never decreases in value (relative to itself at least, it can change value when compared to other countries currency, and inflation can take it's toll, but once again, this is a different topic), whereas treasury bonds can.