Assassination of John F. Kennedy - November 22, 1963
The mutant known as Magneto is implicated in the assassination of John F. Kennedy by a witness on the grassy knoll. Magneto denies direct involvement, sparking the “Free Magneto” movement. Magneto is imprisoned under the Pentagon.
Note: In the new timeline, he insists that the bullet was bent because he was trying to save Kennedy (who is implied to be a mutant).