What would happen legally if a juvenile assasinated the president of the united states?

I was reading a short political fanfic the other day of that peaked my interest. it was about how a 12 year old member of the KKK youth corp sniped president obama. I always know that assassinating the president puts you on death row, but I also know that the juvenile system is extremely different. how would this case be solved? the story ends once the kid pulls the trigger, so would a 12 year old be put on death row? would this be a hate crime? would he just be rehabilitated? what would happen?