Washington DC - Democratic voters across several states head to the polls Tuesday in another test of whether the party's anti-establishment left can extend a run of primary victories into races that could help decide control of Congress in November.
The most consequential contest is in Minnesota, where leftist Lieutenant Governor Peggy Flanagan faces moderate congresswoman Angie Craig for the Democratic nomination to replace retiring Senator Tina Smith.
Flanagan has the backing of Smith and prominent left-wing senators, including Bernie Sanders and Elizabeth Warren, while Craig is supported by Democrats who argue her record winning competitive elections makes her the safer choice for the general election.
"Special interests think they can buy this Senate seat. They've spent $20 million to do it," Flanagan posted on X ahead of polls opening.
"But I have seen what Minnesotans can do when we organize together. So when it comes down to the many or the money, I'm betting on us."
Their clash mirrors a wider argument inside the party over how aggressively to move left as Democrats try to exploit President Donald Trump's weak approval ratings and regain Congress.
Trump's aggressive immigration crackdown has also emerged as a focal point in Minnesota after two US citizens were shot dead in the state during separate encounters with federal immigration officers.
Flanagan has attacked Craig over her support for the Laken Riley Act, a Republican-backed immigration measure, while Craig has emphasized electability and later expressed regret over her vote.
The elections follow Abdul El-Sayed's narrow victory last week over establishment-backed Haley Stevens in Michigan's Democratic Senate primary, which energized progressives, but also exposed how unreliable polling can be in low-turnout contests.
Races to watch in Wisconsin and South Carolina
Wisconsin provides another major test of the left, though in a gubernatorial rather than congressional race.
Democratic socialist Francesca Hong is widely seen as the frontrunner for the party's nomination for governor, despite unease among establishment Democrats and even some leftists over whether she can win a closely divided state in November.
Milwaukee County Executive David Crowley has become the principal moderate alternative, while Sanders and leftist star congresswoman Alexandria Ocasio-Cortez – usually eager to boost insurgents - have notably stayed out of the race.
Hong's candidacy has nevertheless become a symbol of the same leftward pressure that has already toppled established Democrats in New York, Colorado, and Michigan.
Republicans have eagerly seized on those victories, with Trump increasingly portraying November's elections as a choice between Republican "common sense" and what he calls socialist or communist extremism.
Republicans, meanwhile, have their own test of party loyalty in South Carolina.
Senator Darline Graham, appointed after the death of her brother Lindsey Graham, is seeking the Republican nomination for a full term with Trump's endorsement.
Trump held a telephone rally for Graham on Monday, calling her the "perfect person" to carry on her brother's legacy, but rivals have attacked her lack of political experience and argued she inherited her position rather than earned it.