The novella was actually triple nominated, for what may be considered the triple crown in science fiction awards. "Loose Ends" was a Hugo nominee, a Nebula nominee, and on the short list of 1997 stories for the Sturgeon Award.
The story introduces Jeff Harris, who goes back in time to stop the Challenger disaster, but finds himself in November 1963, on the eve of the assassination of John F. Kennedy.
Michael Burstein, reviewing the novella in Tangent, observed that "Paul Levinson has taken the brilliant step of combining the emotional impact of two tragic American events ... But Levinson does much more. He creates a love story set against the evocative portrait of New York City."
*Note added January 11, 2015: Sequel to Loose Ends - "Little Differences" - just published.
*Note added February 7, 2015: Sequel to Little Differences - "Late Lessons" - just published.
And here's Analog 1999 illo by Randy Asplund for "Late Lessons"
What if the Soviet Union survived into the 21st century?
If you're a devotee of time travel, you might also enjoy my Sierra Waters time travel trilogy, published by JoSara MeDia:
words by Paul Levinson, music and recording by John Anealio
Loose Ends cracks Amazon's Top 100 for Time Travel