Actually it was Clinton's idea to have the government invest SS funds in the stock market directly: http://people-press.org/report/70/support-for-clinton-but-no... . That would have been a terrible idea for many reasons. Bush's plan to allow younger workers the option to invest a small portion of their SS taxes would would not have been significantly affected by a fall in the market over the course of a few years.
I was referring more to the boom in 2000 when we thought the stock market could do no wrong, and we were all stupid for putting our savings into things like money market accounts when the Dow was outperforming everything in sight.