PALOS HILLS, Ill. — When Representative Daniel Lipinski, a conservative-leaning Democrat and scion of Chicago’s political machine, agreed to one joint appearance last month with his liberal primary challenger, the divide in the Democratic Party was evident in the audience that showed up.

Mr. Lipinski’s outnumbered supporters were the diminished lunch-pail Democrats that once dominated his Southside district. Those of his rival, Marie Newman, came from the party’s ascendant coalition — young progressives and women like Elizabeth Layden, a Patagonia-clad teacher who explained her opposition to Mr. Lipinski in blunt terms.

“Because he’s a dinosaur, ’cause he’s a phony, ’cause he’s a Republican who claims to be a Democrat,” said Ms. Layden, 49, who has been making phone calls and knocking on doors to help unseat Mr. Lipinski, a seven-term House member, in the primary race this month. “Hello, women’s rights, and hello, my reproductive rights. Get out of my uterus.”

As the midterm election season gets underway with races in Texas on Tuesday and Illinois on March 20, contests like this one illustrate the turmoil of the Trump-era Democratic Party. Democrats need to pick up 24 seats to take back control of the House and are hoping a surge of grass-roots energy, activism and fund-raising at levels unseen since the rise of Barack Obama can help play a crucial role.