stuff the ballot box
Put fraudulent votes in a ballot box, or otherwise cheat in an election. For example, The only way he'll win is if we stuff the ballot box. [Second half of 1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.