WASHINGTON — The narrow victory of progressive doctor Abdul El-Sayed in Michigan’s bitterly fought Democratic Senate primary sets up a defining test of the party’s progressive wing in one of the highest-stakes U.S. Senate contests of the midterms. As Democrats struggle over the party’s post-2024 identity and grapple with how to win back voters, the divide between the party’s progressive and centrist wings has been on display in primary fights. On Tuesday, two progressive congressional candidates in Michigan beat out establishment Democrats in House races — in one case, ousting an incumbent. At least two key Michigan Democrats signaled a desire to move past the primary’s fights. Late Tuesday, Mallory McMorrow, a Michigan state senator who launched her own bid for the seat but suspended her campaign in early July, released an endorsement of El-Sayed.