USD's rally

The USD Dollar cratered as stocks recovered from April - August. Now that stocks are falling, the USD Index has rallied a little:

When the USD Index reached a 2 year low in the past, and then rallied above its 50 dma, the Dollar's forward returns over the next 3 months were more bearish than random. But that's because many of the bearish historical cases occurred in the great 2002-2007 USD bear market:

As for the S&P 500, this did not have a consistently bearish impact. But perhaps this time is different since the USD and S&P have moved inversely thusfar. Then again, correlations work until they don't and can break at any time.