The chart above shows that a leading diagonal may have formed from the March lows. Notice there are 5 distinct, but overlapping, waves that stay within the bounds of the triangle trendlines. If the market had truly bottomed in March, this uptrend could be considered Wave1. Now, we would be in Wave2 down. It would likely drop below 1373 to the 1330-1350 range before starting Wave3.
However, I find this scenario improbable for a couple reasons. First, the decline from the October 2007 high was in 5-waves. 5-wave declines are usually corrected, and then followed by another 5-wave decline that undercuts the previous low (forming a 5-3-5 zig-zag correction). Second, in a leading diagonal, the correct subdivision pattern is 5-3-5-3-5, whereas in this case, each upleg divides into 3 waves.
What would cause me to become bullish? If the recent decline stops where Wave-c = Wave-a and then rebounds above the Wave-a low. This would tell me that the decline was indeed just a 3-wave correction of the new bullish trend. I would look to buy on a rally through the Wave-b top.