In the throes of the Cold War, the Soviet Union was planning to test a massive nuclear bomb in the Arctic Circle.
But in a letter to then-President John F. Kennedy, a young Michigan girl was most concerned about the North Pole's most famous resident.
"Please stop the Russians from bombing the North Pole," 8-year-old Michelle Rochon, of Marine City, pleaded, according to news reports at the time. "Because they will kill Santa Claus."
Kennedy's brief, but reassuring response to Rochon is part of a trove of holiday-themed archival materials being featured this month at the John F. Kennedy Presidential Library and Museum in Boston.
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"You must not worry about Santa Claus," the president wrote on Oct. 28, 1961. "I talked with him yesterday and he is fine. He will be making his rounds again this Christmas."
Kennedy also told Rochon that he shared her concern about the Soviet Union's test, "not only for the North Pole but for countries throughout the world; not only for Santa Claus but for people throughout the world."
Photos of the Kennedys celebrating Christmas in the White House and copies of the family's Christmas cards are among the other holiday keepsakes being highlighted in a seasonal display in the library's lobby.
Rochon, who now goes by the last name Phillips, told The Boston Globe in 2014 that she never thought the letters would resonate the way it did back then, when it turned her into something of a national sensation.
"I was just worried about Santa Claus," she told the Globe.
The Soviets, meanwhile, made good on their threat to bomb the North Pole. Two days after Kennedy penned his letter, they dropped the "King of Bombs," as it was dubbed in Russian.
Reportedly 1,570 times more powerful than the bombs dropped on Hiroshima and Nagasaki combined, it shattered windows as far away as Norway and Finland. It's still considered the most powerful man-made explosive ever detonated.
Kennedy and other world leaders were quick to denounce the bomb test, The Washington Post reports. None of the officials' statements, however, addressed Santa's fate.