In the closely divided Phoenix suburbs that were crucial to Democrats’ recent wins in Arizona, some exhausted voters said they were deliberately tuning out the fractious negotiations in Washington and the threats of a government shutdown.

But others said they had been calling and writing Ms. Sinema for months and now worried that the Democrats’ best chance to advance major policies was slipping away because of their senator.

Over the weekend, the state’s Democratic Party threatened a symbolic vote of no confidence against Ms. Sinema. Dissatisfied Democratic donors and activists are launching a Primary Sinema political action committee to raise money to fund primary challengers in 2024 if she blocks the Democratic agenda in Washington…

Democratic activists believe Ms. Sinema’s political future — and Arizona’s — lies in the growing number of left-leaning Latino and young voters in Phoenix and the fast-growing cities of surrounding Maricopa County, home to about 60 percent of Arizona’s 7.3 million residents. They point to some surveys showing support for Democratic proposals to expand Medicare, provide more child care or expand tax cuts to working-class people.