On a Saturday evening in Michigan, the skies still hazy from drifting Canadian wildfire smoke, hundreds of voters packed into Detroit’s opulent 104-year-old Opera House, rising from their seats to cheer loudly as Senator Bernie Sanders and Democratic Representative Alexandra Ocasio-Cortez took the stage.

As two of the leading figures on the American left, Ocasio-Cortez and Sanders were there to champion Senate hopeful Abdul El-Sayed – a doctor running on a platform of universal healthcare.

His supporters carried signs with El-Sayed’s slogan “Medicare for All”, and wore shirts urging the end of immigration enforcement and US aid to Israel.

But they were not the only ones tuning in.

Voters and politicians across the country are watching to see if El-Sayed can earn the Democratic nomination to run for Senate in November’s midterm elections. His opponent – Congresswoman Haley Stevens – is an experienced politician with deep pockets, thanks in part to large corporate campaign donations.

The two represent the divisions within the Democratic Party as it seeks to take back control of Congress. On one side is the centrist establishment, backed by traditional power players. On the other is the left wing of the party, exemplified by Sanders and Ocasio-Cortez as well as New York City Mayor Zohran Mamdani.

But while left-wing Democrats have seen a wave of victories during this summer’s primaries – including in New York and Colorado – what remains to be seen is if they can claw back support from disillusioned working-class voters, who flocked to President Donald Trump in 2024.

In Michigan – which voted for Democrat Joe Biden in 2020 but Trump four years later – the open Senate seat is a must-win for Democrats.

The seat had been held by one of their own, and if the party hopes to make gains in the Senate, and halt Trump’s agenda, they will need to keep a hold of it. Whoever wins the primary on 4 August will be competing against Trump ally Mike Rogers come 3 November.

At Saturday’s rally, some in the crowd felt hopeful, as Ocasio-Cortez promised El-Sayed represented the “politics of the future”.

But miles outside the venue, other voters were less certain of his ability to beat Stevens – or to secure a victory for the Democrats by touting policies like healthcare for all and staunch opposition to Israel’s military campaign in Gaza.

“This may not be the moment for progressives,” said Colleen Houlihan, a 74-year-old from Ferndale, Michigan who is likely voting for Stevens. “I want radical change in the country, but we’ve got to start with this administration and it’s got to be an electable candidate to get power back in sane hands.”