Senator Tom Carper of Delaware fended off a primary challenge from his left on Thursday, dispatching a political newcomer, Kerri Evelyn Harris, in the latest test of strength between Democratic insurgents and the party establishment.
The most successful statewide politician in Delaware history, Mr. Carper won renomination for a fourth Senate term and what will likely be his 14th consecutive general election victory. He had about 64 percent of the vote with 75 percent of the precincts reporting, according to The Associated Press.
His deep connections in the state he has served since 1976 — as treasurer, at-large congressman, governor and senator — were enough for victory. But Mr. Carper, 71, had to work hard for the right to seek what he suggested could be his last term.
Declaring that the incumbent’s moderate and consensus-oriented politics were out of step with today’s Democratic Party, and insufficient to meet the challenges of the Trump era, Ms. Harris, 38, pushed Mr. Carper to the left. He expressed regret for voting to confirm Brett M. Kavanaugh to a circuit court judgeship, offered his support for decriminalizing marijuana and amplified his criticism of President Trump.
An Air Force veteran-turned-activist, Ms. Harris, 38, sought to tap into the same anti-establishment energy on the left that propelled successful congressional challengers such as Alexandria Ocasio-Cortez in New York and Ayanna Pressley in Boston to victory over incumbents. She campaigned on universal health care and raising the minimum wage to $15, and she lashed Mr. Carper for his pro-business posture and willingness to accommodate Delaware’s financial services and pharmaceutical industries.
But Ms. Harris did not draw the same amount of attention, locally or nationally, and she raised only about $140,000.
Her loss illustrates the difficulty of scaling up primary challenges in statewide races where there is not the sort of readily available coalition — a mix of people of color and younger white progressives — that has lifted other Democratic insurgents this year. While Delaware has a modest black population, it is not a hub for liberal white millennials.
But the success of candidates like Ms. Pressley and Ms. Ocasio-Cortez was clearly on the mind of Mr. Carper. Since his first race in 1976 he had relied on a mix of affability and political pragmatism to find success — 13 victories in 13 statewide races — in one of the country’s most lightly populated states.
He raised more than $3.5 million, airing commercials trumpeting his achievements for Delaware and boasting of all the miles he put on his Town & Country minivan — but also reminding voters of his opposition to Mr. Trump and polarizing cabinet figures such as Education Secretary Betsy DeVos.
And Mr. Carper enlisted his friend and former colleague, former Vice President Joseph R. Biden Jr., to record a radio ad and automated call on his behalf.
Most of all, he relied on the relationships he has built up in the “state of neighbors,” as Delaware politicians call it, a place small enough — with a population of about 960,000, ranking it 45th among all states — where a veteran figure like Mr. Carper can personally meet a sizable number of voters, and an even larger share of the primary electorate.
Even as he won the right to serve a fourth term, though, Mr. Carper suggested he was puzzled by the competing demands he was hearing from Delaware voters.
“I go around the state and I hear two messages: Number one is, why can’t you guys in Washington find a way to work together like we do here in Delaware?” he said after the Labor Day parade in Wilmington Monday. “But the other message is: This guy Trump is no good and you should oppose him with everything you can.”
For a self-declared political centrist, it may have been jarring, and Mr. Carper wondered out loud whether there was “room for us in the middle.”
Ms. Harris argued that the party had passed him by, that his moderate and cautious politics were outdated at a time when the left is ascendant in the national Democratic Party.
Running in a state that has elected a long line of officials who hover between the center-left and center-right, most of them white men, Ms. Harris said Delaware needed a candidate with “a diversity of experience.”
A biracial lesbian who noted she had worked in mostly male-dominated jobs, she called herself “a whole lot of otherness.”
While acknowledging she was facing a steep climb because of Mr. Carper’s financial advantage, Ms. Harris argued she was “changing the definition of what viability means in a campaign” by virtue of the volunteers she had signed up.
“Viability used to mean a whole bunch of money,” she said. “Now, at least here in the state of Delaware, it means a whole bunch of people.”
Her challenge irritated some elements of the state’s Democratic establishment who worried that it presaged an incipient tea party of the left. But other Delaware Democrats said there was an upside to the competition.
“Maybe Carper needed a little bit of a kick in order to say, ‘Hey, I’ve really got to do things and pay attention,’” said Paul Thornburg, the second-ranking official with the state Teamsters.