The first US president to be assassinated was Abraham Lincoln in 1865. The last – so far – was John F Kennedy, fifty years ago today. A century separated the two men’s election – 1860 for Lincoln, Kennedy in 1960.
Most Americans still refuse to believe Kennedy’s killer, Lee Harvey Oswald, acted alone, insisting he was either framed or part of a conspiracy. Curiously, many believe a lone nut did murder Lincoln – whose assassination actually was part of a documented plot[*].
Kennedy’s death was quickly followed by the swearing in of Vice President Johnson; thus, he became the first southerner to hold the office of president since Lincoln was succeeded by his VP – Johnson[†].
Both Presidents Johnson, governing in difficult times, became increasingly unpopular and mistrusted. Bitter, facing opposition from within their own parties and almost certain defeat, neither sought a second term.

[*]John Wilkes Booth was head of a small group of radicals and Confederate spies. They planned, initially, to kidnap Lincoln on the road to his summer residence and hold him to ransom for the South’s independence. When the President’s travel plans were cancelled, they settled on a synchronised round of executions to decapitate the Union Government.
While Booth was shooting Lincoln, Secretary of War Stanton was set upon in his bed – where he’d been recuperating from a carriage accident. Stanton escaped serious injury but his son was stabbed wrestling with the attacker, who fled.
Secretary of State Seward survived because his would-be assassin lost his nerve at the last moment.

[†]Andrew Johnson of Tennessee. Kennedy’s successor was, of course, Lyndon Baines Johnson of Texas.