Primaries in the Midwest have become a high stakes proving ground for progressives

An attendee props up a sign with Democratic U.S. Senate candidate Abdul El-Sayed's slogan highlighting his progressive policy of Medicare for All on July 25 in Ferndale, Mich. Emily Elconin/Getty Images hide caption

The Democratic primary for Michigan's 7th Congressional District puts the high stakes for the party in the midterm elections on full display. The district is one of just 18 toss-up districts, making the Republican-held seat a top target for Democrats trying to retake the House.

That's why it has attracted candidates including a former U.S. ambassador to Ukraine, a retired Navy Seal and William Lawrence, a co-founder of the climate activist group the Sunshine Movement.

Lawrence thinks his outsider approach and willingness to criticize his own party is just what this competitive district needs to win in November.

"What I hear is people are fed up," Lawrence said in an interview with NPR. "They're ready for change and they don't feel that either party has been representing their interests in DC."

This year, far left challengers have notched upset wins against Democratic incumbents in deep blue congressional districts from New York to Colorado.

That brand of progressive politics is about to get its biggest test yet, in midwestern swing states and competitive districts that could decide control of Congress. Democrats voting in primaries this month in Michigan, Wisconsin and Minnesota are wrestling with a question that has divided the party going back at least to 2016.

It's about who has a better shot of winning in purple states and toss-up districts: a populist progressive outsider or a moderate favored by the Democratic establishment.