This was a clincher—assorted worthies sent their own medals back in protest but everyone else was delighted.
early 14c., "person or thing that clinches" (i.e., secures nails by bending down or riveting the pointed end), late 15c. as a class of shipyard worker; agent noun from clinch (v.). As a type of nail, from 1735; as a conclusive statement, argument, etc., 1737.
The deciding or conclusive element; the BOTTOM LINE: One smudged fingerprint was the clincher (1830s+)