I analyzed all US crises for the last 100 years. And that's my conclusion.
Key Levels: 211 - if the price will be below this line it is the beginning of the crisis (time to short) 151 - Bottom of the crisis (time to buy around this level. 25% from your `deposit` each week with a limit order. Try to get the best price possible) 80-70 - Worst case scenario. Little chance that we will see this prices.