A young Chicago progressive is challenging an established liberal for Congress in a race that reflects Democratic Party divisions

CHICAGO — On a recent Sunday afternoon, 31-year old Kina Collins strode up the front steps of tidy bungalows in the Galewood neighborhood on Chicago’s West Side to introduce herself to voters in the hopes they will make her their next representative in Congress. Repeatedly referring to their current congressman, U.S. Rep. Danny Davis, as a “25-year incumbent,” Collins encouraged the voters to open their minds to the idea she could — and should — do the job. “He’s been my representative since I was 5 years old,” Collins recited to the voters as they stood on their front stoops. “We know that it...