Abrahan Lincoln was elected President in 1860.
John Kennedy was elected in 1960.
Lincoln's successor - Andrew Johnson - was born in 1808.
Kennedy's successor - Lyndon Johnson - was born in 1908.
Lincoln's killer - John Wilkes Booth - was born in 1839.
Kennedy's killer - Lee Harvey Oswald - was born in 1939.

Lincoln's secretary was called Kennedy, while Kennedy's secretary was called Lincoln.
(Note: the above fact is apparently in some doubt. For more info, click here)
The names Lincoln and Kennedy each contain seven letters.
Lincoln's and Kennedy's successors both had the surname Johnson.
The names Andrew Johnson and Lyndon Johnson each contain thirteen letters.
The names John Wilkes Booth and Lee Harvey Oswald each contain fifteen letters.

Lincoln and Kennedy were both killed on a Friday.
Both were killed in the presence of their wives.
Both were shot from behind and in the head.
Booth shot Lincoln in a theatre and hid in a warehouse.
Oswald shot Kennedy from a warehouse and hid in a theatre.
Both assassins were killed before being brought to trial.

Lincoln and Kennedy were both directly concerned with Civil Rights.
Booth and Oswald were both Southerners favouring unpopular ideas.

And finally, the most eerie coincidence of all...
A week before his death, Abraham Lincoln was in Monroe, Maryland.
A week before his death, John Kennedy was in Marilyn Monroe.

(Ba-dump-bump.)