If he defeats Horiuchi's chosen Democratic successor, Jenny Wilson, it would give Republicans a veto-proof majority on the council.
The convention was tough, meanwhile, for two county incumbents: auditor Greg Hawkins lost his bid for a second term while assessor Kevin Jacobs was forced into a primary election.
"There is no accountability for your tax dollars," said Scott Tingley, the challenger in the auditor's race, criticizing Hawkins' "checklist" method of auditing. Tingley, who promised to improve the office's relationship with the county council, won 69 percent of the delegate vote to Hawkins' 31 percent.
In the assessor's race, second-time challenger Jake Parkinson won 53 percent of the approximately 2,200 delegates.
"I'm running under the banner that life isn't always fair but your market value should be," said Parkinson, a deputy Tooele County assessor.
Jacobs, an assessor's office employee who was named to the top spot in September when his boss left for a Church of Jesus Christ of Latter-day Saints mission, got 47 percent. Both men will be on the primary ballot.
The convention was slowed somewhat by technical issues and questions about security as delegates voted online.
Utah Attorney General Sean Reyes was applauded in his speech for his court battle to keep the state's ban on same-sex marriage, Amendment 3, which he argued this week in front of the 10th Circuit Court of Appeals in Denver.
"It is worth the fight, it'll always be worth the fight to stand up … [for] the sovereign right to make that determination based on your voice and your vote."
Gov. Gary Herbert also invoked state's rights on that issue and on the Bundy Ranch standoff in Nevada.
"I just got word that the BLM is backing down," he said. It does point to the need, he added, "to stand up for state [sovereignty]."