Now, there's a difference between deceleration in prices, and a decline in prices.
 
There's a difference in controlling inflation, and inducing deflation. 
 
The Fed's job is price stability.  Does price stability mean getting inflation back to their target level (of 2%)?  Or does it mean returning prices back to trend, which would mean a period of deflation?
 
Regardless of the Fed's intent, their are some that think a swing back to the deflationary era is coming.  Among those that share the viewpoint: Elon Musk and Cathy Wood.  
 
The Fed has told us explicitly that they are doing whatever it takes to get inflation back down to their target of 2% (inflation is their goal, just much lower inflation). 
 
With this next chart in mind, it seems implausible that deflation could return anytime soon.