Most people don't know how close it came in the Depression, actually. The only things that really saved our bacon is that we weren't dependent on imports to maintain basic infrastructure, and we didn't have much of that.

Let's play a bit of what if:

Serious drought in the west, leading to near total crop failure for three or fours years, and a serious issue with Mexico over water rights. Most of your west coast cities start to have massive water issues, in some cases leading to the history books would call the "water riots", along with food shortages. As the possibility of a war with Mexico increases, toss in race riots and lynchings. Without crops to export, our trade balance worsens, particularly when the plains and midwest turn into a dust bowl due to lack of ground cover and moisture, sending the American dollar down against global currancies.

Eventually, we'd collapse- we can't rebuild ourselves if the dollar drops like mark just after WWI. If trade and crops go in the toilet together, that will all the pretty lady in the harbor wrote, becuase someone will try to sell her as scrap. <img src="/images/graemlins/frown.gif" alt="" />