Fixing The Votes...
Donald has found out the Forellis are responsible with vote counting, so you need to "fix" their machines.
...Fixing The Riggers
Head to the voting station in Fort Staunton after getting the Flamethrower from Phil Cassidy's. There are a number of voting ballots and two printing machines and you need to set them alight. After doing so, you have to kill the Forellis that try to run away. Once they're dealt with, get out of Fort Staunton to complete the mission.
You have unlocked Phil Cassidy's Fully Cocked Gun Shop, where you can buy these wares:
Shotgun - $1500
M4 - $5400
Flamethrower - $5500
Rocket Launcher - $9000