The Democratic party faces a crucial test of its direction today as voters in the midwestern swing state of Michigan decide whether to nominate for US Senate a progressive candidate advocating for universal healthcare or an-establishment-backed moderate.

The state’s Democratic primary is the latest high-profile battle over the party’s future, as it seeks to chart a course back to power in Washington following Donald Trump’s victory in 2024.

Leftwing candidates have surged in Democratic primaries in solidly blue areas across the country in recent months.

Some congressional primary races in Michigan will also offer a sense of where the party is headed as it looks to take back control of US Congress from the Republicans.

Progressive Abdul El-Sayed, a 41-year-old former public health official, has led in recent polls against his moderate rival, US representative Haley Stevens, a 43-year-old who first came to Congress after flipping a red seat.

A flood of more than $40m in outside spending has come into the race to support Stevens or attack El-Sayed, including from groups associated with the American Israel Public Affairs Committee (Aipac), a pro-Israel lobby.

The winner of Tuesday’s Democratic primary will face Mike Rogers, a former congressman from the state who was also the Republican nominee for US Senate in 2024, when he lost to Elissa Slotkin.

The Michigan US Senate seat is critical for Democrats in their dark-horse quest to retake the upper chamber, where Republicans currently hold 53 of the 100 seats.

Michigan is not the only state with primaries on Tuesday. In Missouri, voters will weigh whether to nominate former US representative Cori Bush, who is running to return to the chamber against Wesley Bell in a race punctuated by the war in Gaza and outside spending by pro-Israel groups.

And in Washington state, voters will decide which two candidates to elevate in the third congressional district, where blue-dog Democratic representative Marie Gluesenkamp Perez is seeking re-election amid challengers from both sides of the aisle.

Congressional seats, including one in Slotkin’s former district, are also in the mix in Michigan, with further tests of progressives’ rise.

The progressive US senator Bernie Sanders has boosted El-Sayed and two progressive challengers in congressional races. In the Lansing-area seventh district, Sanders backed William Lawrence, a community organizer who co-founded the Sunrise Movement, over former US ambassador to Ukraine Bridget Brink and Matt Maasdam, a former US Navy Seal.

Maasdam received Slotkin’s endorsement in the race for the purple district, currently held by Republican Tom Barrett. In the 13th district, Sanders boosted state representative Donavan McKinney, who is running against incumbent Democratic representative Shri Thanedar in the Detroit-area district.

On the right, Republicans will figure out if they want to nominate John James, a US representative with Donald Trump’s endorsement, or businessman Perry Johnson to face Jocelyn Benson, the secretary of state and likely Democratic nominee for the governorship.

James has led in polls, but late grassroots energy has given Johnson some momentum. Governor Gretchen Whitmer, a Democrat, served for eight years and faced term limits preventing another run for the high office.