A deviation in trend from the interest rate expectations pushed the index lower throughout 2017. The hawkish outlook of the fed & already high interest rate (compared to other major central banks) haven't stopped a push lower. Always good to keep a look at the dollar index before making trades involving it.
Technicals
The fairly recent break below the 200DMA gave expectations for a continuation of the 2017 bearish sentiment.
Price currently sitting around an area that has acted as a good pivot point all the way back to 1999
.382 retrace off 2008 lows acted as support in september 2017