Overview: Headlines for June 23, 2016; 'Let Us Vote': Rep. John Lewis Leads Historic Democratic Sit-in for Gun Control Legislation; Democratic Effort to Tie Gun Purchase to Terror Watchlist: A First Step or a Dangerous Precedent; In Wake of Orlando, Florida Rep. Alan Grayson Revives Efforts to Implement Assault Weapons Ban; Daughter of Slain Virginia Tech Professor: We Must Address Our Nation's Gun Violence Epidemic; Colombia & FARC Agree to Ceasefire in Historic Peace Deal, Begin Long Process of Implementation