Violent, repeat criminals should be put away for a long time, Congress quite reasonably decided in 1984.  But the devil is in the details, and the Armed Career Criminal Act has been an interpretive problem for a long time.  What exactly is a "violent felony or serious drug offense"?  Jess Bravin has this article in the WSJ on today's argument in Johnson v. United States, No. 13-7120.  The transcript is here.