Duncan said the politics of lawmaking needs to be changed. The Cumming resident, who likes to position himself as an outsider, served five years in the state House before resigning last year to focus on his campaign.
Duncan said if elected, he would put an end to legislative horse trading.
Amico, who is the executive chairwoman of a transportation company, touts her business experience as the reason Georgians should vote for her.
The winner of the July 24 runoff will face Amico in November.