SP500 is retesting the green potential base channel line as shown in Chart 1. This support holding likely offers an opportunity for SP500 to deliver an overthrow in the context of the expanding diagonal triangle shown in Chart 1, or a more bullish third wave up relative to the October 2014 low (Chart 2 green).
A decisive breach of the this support likely suggests a larger degree correction (i.e. against the 1820.66 low or worse, rather than against the 1980.90 low). In that case, a decline toward the green (b) in Chart 1 or the blue wave  in Chart 2 is likely in progress.
Chart 3 (INDU) and Chart 4 (SPX) track the current decline on the assumption of a corrective pullback.