The Soviets were apparently prepared to kick off the festivities with an atomic bomb pre-positioned in their own embassy in the District of Columbia. It was, so the story goes, assembled from components brought in by diplomatic bag.
US authorities and journalists sufficiently intimate with Pres. Kennedy to have lunch at the White House were well aware of this information but withheld it from the American public for over forty years.
Time finally revealed the story in a manner apparently calculated to minimize public attention and comment. No other publications picked up the story.