Particularly confusing is the blue line in the graphs

Won't have much time for livejournal in the next couple of days. In the meantime I'm linking a long post by Brad DeLong that I don't understand well after one reading, in case any of you would like to explain it to me:

Today In Financial History

The purpose of stage III policies is to boost demand relative to supply for risky assets, and thus to operate on the margin that is the spread in prices and yields between safe assets like Treasury securities and the risky assets whose falling prices are threatening the stability of the financial system and the macroeconomic flow of investment.