Bobby Rush wants to pick who gets his seat. 19 people disagree.

“I know my entire district better than anyone else,” Rush said in an interview. “And so, I recruited someone who I thought fit my district like a hand in glove. Who, in some sense, is made or manufactured for my district to replace me.”

Yet in the weeks since his January endorsement of Karin Norington-Reaves, a nonprofit executive with no significant political experience, the Democratic primary for the 1st Congressional District has only gotten more crowded. Alongside Norington-Reaves, there are now 19 other Democrats — small-business leaders, pastors, a . . .