On the plane back to Washington, in her pink Chanel suit, caked with her husband’s blood, Jackie Kennedy resisted all suggestions from aides that she clean herself up. Instead, she just said, “Let them see what they’ve done.”

But for the half century since John F. Kennedy’s assassination in Dallas on Nov. 22, 1963, the most famous artifact from that day, one of the most recognizable articles of clothing ever worn, has been seen by almost no one. Now preserved by the National Archives in a climate-controlled vault outside of Washington, it is subject to Kennedy family restrictions that it not be seen for almost a century more.

If there is a single item that captures both the shame and the violence that erupted that day, and the glamour and artifice that preceded it, it is Jackie Kennedy’s bloodstained pink suit, a tantalizing window on fame and fashion, her allure and her steely resolve, the things we know about her and the things we never quite will.

That Mrs. Kennedy is so closely linked to an item of clothing is fitting. In nearly three years as first lady, she had gained universal celebrity for her youthful style. Politically, it meant huge crowds whenever she accompanied the president. But for Mrs. Kennedy, who felt vulnerable, fashion gave her a sense of separation from the public’s gaze. It was armor.