The Obama administration in 2013 announced it would not stand in the way of states that legalize marijuana, so long as officials acted to keep it from migrating to places where it remained outlawed and out of the hands of criminal gangs and children. Sessions is rescinding that memo, written by then-Deputy Attorney General James M. Cole, which had cleared up some of the uncertainty about how the federal government would respond as states began allowing sales for recreational and medical purposes.
Curious to know how you all feel about this? Personally, I believe state law should almost always take precedent over federal law, and that the move made by the Obama administration was beneficial to that approach. This appears to be an attempt to erode the weight of states' laws. Jeff Sessions' thoughts about marijuana are probably worthy of a separate discussion; that guy is off his fucking rocker comparing it to heroin.