The alternating bouts of rising and falling oil prices have doubtless been a significant contributor to the periods of deceleration and acceleration of U.S. economic activity over the past year. Despite the uneven character of the expansion over the past year, the U.S. economy has done well, on net, by most measures.
If the price of oil does not continue to go down (it cannot go down indefinitely), we will see a jump in inflation in the last quarter of this year. But we may have before that some months of negative inflation. Until now we have not seen a reason to doubt that the programme will work.