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swinging voter

British  

noun

  1. Also called (esp in Britain): floating voterinformal a person who does not vote consistently for any single political party

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

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Distinct from the more traditional swinging voter, authors Ron Booker and Eric Sidoti see these 18-24-year-old voters as permanently unaligned and developing "electoral habits of their own making".

From BBC