It doesn’t require a full scale Great Depression style meltdown, the ‘downturn’ of 2008 caused significant difficult for many, it simply requires a sharp enough retraction of Investment Capital. That retraction is already in progress as the retirement rate for Boomers escalates and more of them begin selling their stocks and bonds; either directly or through their retirement instruments like 401ks and Pensions.
I’m not a doomer but I am fairly convinced that 401ks are a timebomb.