The story
Blend of dummy + gerrymander, coined by Bernard Grofman & Thomas L. Brunell in 2005.
Etymology from Wiktionary, CC BY-SA 4.0.
dummymander
Today it means: A gerrymander whose narrow margins—intended to electorally benefit the gerrymandering party by consolidating expected opposing voters and more widely distributing expected supporting voters—backfire and actually end up helping the opposing party. Full definition →