The stakes of the campaign were on display during a recent morning of door-knocking in Tucson, where Mayor Regina Romero introduced voters to Mendoza, the Democrat challenging Ciscomani in a district that has narrowly favoured Republicans in recent cycles.
Approaching one young resident, Romero handed over a pamphlet and listed Mendoza's virtues. The man stood stone-faced until she mentioned Mendoza's record as a US marine. His eyebrows raised as he looked over the brochure: "This is cool."
The exchange offered an early sign of the strategy Democrats are running in the district. Congressional district six is a swing seat in a swing state, where more than a third of residents identify as independents and voter identification is weak. It tethers parts of liberal Tucson to a stretch of conservative countryside dotted with saguaro cactuses that runs toward New Mexico.
Democrats see a genuine opening. The national mood has turned sharply against Donald Trump amid soaring costs and an unpopular war with Iran, and the party believes it has both a favourable environment and the right candidate to tip the balance in the desert battleground.
The young man declined to say how he planned to vote and asked not to be named, citing privacy concerns. But for the mayor, the brief interaction marked a victory, and a sign that Mendoza's military background could break through with voters who might otherwise tune out.