Thomsen, Brian M. "Bloodstained Ground"
What if: Custer was elected president after his victory at the Little Bighorn.
Summary: Failed novelist and journalistic hack Sam Clemens is assigned to write a memorial following Custer's assassination, but his interviews of Autie Reed and Captain Reno reveal the sickening facts behing the Custer legend.
Published: In Alternate Generals (eds. Harry Turtledove and Roland Green), q.v.; and We Could Do Worse (audiobook, ed. Martin H. Greenberg), q.v.