With early voting under way in Arizona, Sinema and McSally are in a dead-heat race. If Sinema wins, she will hold an important seat for embattled Senate Democrats and offer evidence that this solid red state can turn purple. But her campaign will also test a hypothesis about the Democratic Party’s future: The way to win, at least in conservative states, is to move aggressively to the middle.

[Read: A Republican victory in Arizona sets off alarms in the GOP.]

Sinema’s strategy is partly a bet on where the margin of victory for Democrats lies in elections: in the center, or on the left? Some Democrats believe that a fired-up progressive base will make the difference in tight races against Republicans. Beto O’Rourke, who is running against Republican Senator Ted Cruz in Texas, has become a lefty celebrity for his calls to demilitarize immigration enforcement, legalize marijuana, and banish donations from political-action committees. Sinema, by contrast, has started no such national firestorm. “She’s not hitting the progressive G-spot in the way that people want,” as one political operative in the state wryly put it.

To some extent, Arizona has its own test case of this progressive Democratic vision this year, which played out 200 miles away on the day Sinema was in Yuma. Bernie Sanders had come to town to campaign for David Garcia, the Democratic nominee for governor. Throngs of screaming students packed into an auditorium at Arizona State University, near Phoenix; a line of disappointed latecomers stood along the barrier gate outside, hoping to glimpse the 77-year-old democratic-socialist senator. As Sanders worked the crowd at the end of the event, Garcia trailed him a little awkwardly, hoping to catch some of the students’ outstretched hands.

Garcia is the education guy in this election: He has closely aligned himself with the “Red for Ed” movement that led thousands of teachers to strike for higher salaries and better funding for their schools, creating a major challenge for the current governor, Doug Ducey. His rhetoric on immigration is left of Sinema’s: He has called for the abolition of Immigration and Customs Enforcement, the federal agency that enforces immigration laws, and his campaign strategy has focused on mobilizing Latinos and young people. His approach appealed to Anahi Montes Lima, a 19-year-old first-time voter from Wittmann, Arizona, who didn’t know much about Garcia before the rally. “To know that there’s people that support Muslims, and also people like me, like immigrants, makes me feel good,” she told me.

Even though they’re both Democratic candidates for statewide office in Arizona this year, Sinema and Garcia have refused to endorse each other. When I asked Garcia about this backstage at the rally, he challenged the premise of my question. “I have no idea what disunity you’re talking about, to be frank with you,” he said. “I think it’s a Bernie-Hillary narrative that people are trying to play up.” Their campaign visions complement each other, he said, and the Democratic Party “has a lot of different faces to it.” Ultimately, though, he believes that “standing with … the communities most affected” by state-level policies “is what’s going to get people out to vote.”