Who was the first president assassinated while in office?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'INTERNAL', 'name_': 'Q30', 'id': 0, 'label': 'United States of America'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q11696', 'id': 1, 'label': 'President of the United States'}, {'type': 'INTERNAL', 'name_': 'Q851', 'id': 2, 'label': 'Saudi Arabia'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q3882219', 'id': 3, 'label': 'assassination'}, {'type': 'INTERNAL', 'name_': 'Q192778', 'id': 4, 'label': 'Rafic Hariri'}, {'type': 'INTERNAL', 'name_': 'Q407184', 'id': 5, 'label': 'Air Force One'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q179969', 'id': 6, 'label': 'Air Force One'}, {'type': 'INTERNAL', 'name_': 'Q7766710', 'id': 7, 'label': 'The Stormy Present'}, {'type': 'INTERNAL', 'name_': 'Q757963', 'id': 8, 'label': 'assassination of Martin Luther King Jr.'}], 'links': [{'name_': 'P17', 'source': 0, 'target': 0, 'label': 'country'}, {'name_': 'P1906', 'source': 0, 'target': 1, 'label': 'office held by head of state'}, {'name_': 'P530', 'source': 0, 'target': 2, 'label': 'diplomatic relation'}, {'name_': 'P27', 'source': 4, 'target': 2, 'label': 'country of citizenship'}, {'name_': 'P509', 'source': 4, 'target': 3, 'label': 'cause of death'}, {'name_': 'P495', 'source': 5, 'target': 0, 'label': 'country of origin'}, {'name_': 'P138', 'source': 5, 'target': 6, 'label': 'named after'}, {'name_': 'P921', 'source': 7, 'target': 2, 'label': 'main subject'}, {'name_': 'P840', 'source': 7, 'target': 6, 'label': 'narrative location'}, {'name_': 'P17', 'source': 8, 'target': 0, 'label': 'country'}, {'name_': 'P31', 'source': 8, 'target': 3, 'label': 'instance of'}]}