Republican Rep. Jeff FlakeJeff FlakeMcCain’s primary challenger asks him to step aside after diagnosis Sen. Flake's GOP challenger: McCain should resign Senators who have felt McCain's wrath talk of their respect for him MORE has been an outspoken opponent of earmarks in Congress and a strong supporter of the ban. The issue came up in their first debate, when Carmona defended the use of earmarks in certain situations, arguing that "all earmarks are not pork" and that the ban is contributing to congressional gridlock.

The conservative Club for Growth also targeted Carmona's position in favor of earmarks in an ad released earlier this week.

Flake and Carmona are locked in one of the most contentious Senate battles, and the Democrat has shown surprising strength in a red-leaning state. The competitive nature of the race have caused both Democratic and Republican outside groups to invest millions of dollars in the race in recent weeks.

Watch the ad: