spare voter
n.— «Then there’s the fact that a candidate needs to have the support of at least 15% of the voters in a precinct before qualifying for any of its delegates. Backers of a candidate who doesn’t receive the requisite support become what are artlessly referred to as “spare voters”—that is, voters who are free to throw their support behind a second candidate.» —“Comment is free…I hate Iowa” by Conor Clarke Guardian Unlimited (United Kingdom) Jan. 2, 2008. (source: Double-Tongued Dictionary)