“This is part of the reason Donald Trump won,” Mr. Lipinski said in an interview, adding, “Democrats have chased people out of the party.”
In California, party activists at the state Democratic Convention last week rejected Senator Dianne Feinstein, a moderate lawmaker, refusing to formally bless her re-election. In Texas, the Democratic Congressional Campaign Committee opened fire on a progressive candidate, Laura Moser, posting negative research to blunt her rise in fear that a victory by her in Tuesday’s primary race could doom the party’s bid for a suburban Houston district in November.
But the battle to define the party is playing out most vividly in overwhelmingly safe House districts around cities like Boston, Chicago and New York, where younger liberals, often women, people of color or both, are confronting men who are products of a clubhouse politics where fealty to the organization was paramount.
And no lawmakers may be more vulnerable to the rising left than Mr. Lipinski and, in Massachusetts, Representative Michael E. Capuano, a far more liberal Democrat who is nevertheless confronting a restless electorate in his Boston-based district.
Mr. Lipinski, opposed to abortion and uneasy with gay rights, is locked in a bitter campaign with Ms. Newman, a former marketing consultant who has backing from powerful liberal groups such as Naral Pro-Choice America and the Human Rights Campaign.
Mr. Capuano, who is serving his 20th year in Congress, is a down-the-line progressive, who has drawn no opposition so far from national liberal groups. But he has stirred a challenge from Ayanna Pressley, the first black woman elected to the Boston City Council. In a district once held by John F. Kennedy and Tip O’Neill, where college campuses abound and minority communities now make up most of the population, Ms. Pressley argues that voters should demand an activist lawmaker who is more than a “reliable vote.”
Mr. Lipinski was bequeathed his heavily Polish and Irish district in Chicago around Midway Airport and the South Side by his father, William Lipinski, a former ward boss and representative. The two Lipinskis have held the so-called Bungalow Belt seat for 35 unbroken years.
But as in Mr. Capuano’s district, where there is now more nostalgia for Mr. Obama than Camelot, this stretch of Chicagoland is rapidly changing.
Gentrifying precincts around what was Comiskey Park in the Bridgeport neighborhood are now filled with Wi-Fi-hungry hipsters. The elder Lipinski’s old ward headquarters now sit next to a Puerto Rican restaurant, a reminder that over 30 percent of the district is Hispanic.
Yet there are still elements of the fish-fry-Friday voters, the Catholic demographic that political veterans here still call “white ethnics.”
Wearing a Notre Dame hat and standing apart from the attendees at the candidate forum was Jack Nevin, an Illinois Department of Transportation employee who as a child attended the same parish as the Lipinski family and now lives in suburban Lamont.
“I’m a pro-life guy, born and raised Catholic,” said Mr. Nevin, by way of explaining why he was backing the incumbent. “Win or lose, he’s standing up for his beliefs.”
Ms. Newman used the forum to lash Mr. Lipinski for being out of step with the district, a drumbeat that prompted him to claim she was fomenting “a tea party of the left” that was pushing liberal “fantasies.”
But it is Mr. Lipinski who is testing just how much today’s voters in the Democratic primary contest are willing to accept in a safe seat. In addition to his deviation from orthodoxy on abortion and gay rights, he also opposed the Affordable Care Act and until recently did not support a $15 minimum wage or offering legal status to children brought to the country illegally.
“I am running with the district. I’m not voting against the district,” Ms. Newman said.
Her energetic campaign has drawn the support of a host of Washington-based progressive groups, some of which are funding attack ads and mailers against Mr. Lipinski. And she has lured Representatives Luis V. Gutiérrez and Jan Schakowsky of Illinois to oppose their colleague, a rebuke that has angered some moderate Democrats.
Representative Kurt Schrader of Oregon, who leads the political arm of the centrist Blue Dog caucus, has complained to the head of the Democratic Congressional Campaign Committee about the intervention of Ms. Schakowsky and said he would seek a rule change so that members like her who have formal positions on the committee cannot oppose incumbents. “That’s just wrong, and we’re going to change that,” he said.
But the Washington contretemps are just a stand-in for a much weightier debate about the future of the party.
Mr. Lipinski, who makes no apology for opposing the health law, has embraced donations from anti-abortion Republicans helping fund a “super PAC” in his favor and says it is Ms. Newman’s ardent support for abortion rights that is “extreme” for the district.
Ms. Newman is careful to focus on economic issues and inveigh against “the Lipinski dynasty.” But what animates her campaign are matters of identity that are galvanizing Democrats in the Trump era well beyond Chicago.
Her headquarters, not far from the elder Lipinski’s old clubhouse, is filled with signs trumpeting “Intersectional Feminism” and L.G.B.T.Q. rights. When she stopped recently to rally phone-bankers, one volunteer wore a T-shirt demanding “Reparations Now,” a reference to the movement by African-Americans to retrieve compensation for slavery.
Speaking to her supporters, Ms. Newman invoked her transgender daughter.
Over a diner lunch, where her Mercedes stuck out in the parking lot, she said a victory over Mr. Lipinski this month would echo across the country.
“We need to have more diversity across people of color, gender and types of folks,” Ms. Newman said. “We can’t have all millionaires, billionaires, businesspeople and doctors in Congress.”
Unions are divided: Ms. Newman has the support of the more diverse service workers and teachers while Mr. Lipinski retains the backing of the building trades.
A similar gulf exists in Mr. Capuano’s district.
Though the primary race is not until September, Ms. Pressley’s candidacy has already roiled the party in Massachusetts, a rigidly hierarchical and predominantly white organization that is closely intertwined with organized labor.
In an unusual show of deference to Ms. Pressley, two of the state’s highest-profile Democrats, Senator Elizabeth Warren and Representative Seth Moulton, said they would stay neutral rather than back their colleague in Congress. Setti Warren, a former mayor of Newton who is the leading Democratic candidate for governor, endorsed Ms. Pressley. Damali Vidot, a Pressley supporter who is the president of the City Council in Chelsea, said there had been private pressure on Democrats not to buck Mr. Capuano.
But Ms. Vidot said with a smile that she was undeterred. “I’m with the new energy,” she said. “We need someone that understands the struggles of families in different neighborhoods.”
Mr. Capuano is expected to mobilize a powerful group of supporters on his side. He counts Boston’s popular mayor, Martin J. Walsh, as an ally, and Mr. Walsh has signaled he will back Mr. Capuano with his political operation, according to three people briefed on his plans, who spoke on the condition of anonymity because Mr. Walsh has not yet issued an endorsement. Representative Joseph P. Kennedy III, perhaps the state’s best-known House Democrat, is behind Mr. Capuano.
Mr. Capuano, 66, is one of three Democratic members of Congress facing primary opponents in Massachusetts, and he appears to be the most endangered. In an interview, Mr. Capuano acknowledged that he faced a new kind of race in a “significantly different” political environment, and said he was prepared to defend a record of assailing Mr. Trump that includes two votes in favor of impeachment.
“My district is upset,” Mr. Capuano said. “They don’t like the Donald Trump agenda, and I’ve been as vocal as I can be.”
Ms. Pressley, 44, has moved aggressively to cast Mr. Capuano as a figure of the past. At an event shortly after she announced she would run, she delivered a thematic broadside against Mr. Capuano without ever mentioning his name, depicting him as a well-meaning but too-conventional politician.
“We can’t play small ball and hang our hats on good votes on bad bills that pass,” Ms. Pressley declared, to cheers from a crowd of more than 200 in a purple-lit barroom.
Ms. Pressley said the district had “changed a great deal” over the last two decades. “The only thing that hasn’t changed,” she jabbed, “is its representation.”
Even in some traditionally Capuano-friendly quarters, there is a recognition that Ms. Pressley represents a kind of challenge the congressman has not faced before. Harris Gruman, the executive director of the Service Employees International Union’s state council in Massachusetts, praised Mr. Capuano as a “very active” ally, but he noted his union’s membership was “predominantly people of color and women” and said its endorsement would probably be up for grabs.
“We are in a special moment, too, historically, with Trump as president and a sense of racial and social injustice at a heightened level,” he said.
Back on the South Side of Chicago, Ms. Newman fit right in as she spoke to voters at the Jackalope Coffee and Tea House, a few blocks away from the old bungalow of former Mayor Richard J. Daley.
Mr. Daley, the iron-fisted personification of 20th-century machine politics, would have found the array of MacBooks, ironic mustaches and turmeric ginger-pumpkin chais as fantastical as the mythical animal from which the cafe takes its name.
“There’s certainly an old guard, but there’s also a rising number of young people in the city and young people here,” said John Briggs, 47, a history professor, who liked what he heard from Ms. Newman. “There’s an alienation from the machine.”