Supporters react as Sen. Thomas R. Carper (Del.) prepares to give a victory speech after defeating progressive political newcomer Kerri Evelyn Harris in the Democratic U.S. Senate primary. (Suchat Pederson/News Journal/AP)

In July, when national attention started to turn to Kerri Evelyn Harris's insurgent run for the U.S. Senate from Delaware, her campaign had something concrete to offer reporters: a win number. Alexandra Rojas, the co-director of Justice Democrats and the guru behind Democratic congressional candidate Alexandria Ocasio-Cortez's data operation in New York, told The Intercept that it would take 26,000 votes to beat Sen. Thomas R. Carper (D-Del.) in the Democratic primary.

"The campaign, she said, has already identified roughly the same number of supporters as Ocasio-Cortez had when Rojas began working for her a month out from the election in New York,” reported The Intercept's Ryan Grim, in the first of several articles about the Carper-Harris race. “From there, with an aggressive final push, they were able to quadruple the number of identified supporters."

It sounded doable. Ocasio-Cortez had won her primary with just 15,897 votes; Delaware was holding an unusual Thursday primary, in September. As late as this week, both campaigns were talking about a turnout scenario where maybe 50,000 of Delaware's 327,149 registered Democrats would cast ballots. Harris blew past her win number, with 29,406 votes.

So why did Carper win by 30 points? Democrats broke records, with 83,039 Democrats hitting the polls — a turnout of 25.3 percent, and the highest midterm primary turnout ever in Delaware. That was only slightly less than the 93,640 Democrats who voted in the 2016 presidential primary. By contrast, Republicans — with a competitive primary of their own, cast just 37,869 votes, down from 69,892 in the presidential primary.

The story of the left's defeat in Delaware is just that simple. It was not a surprise that Carper, an affable and omnipresent politician who's won 13 statewide elections, had the votes to win. It was surprising, to his opponents, that so many Democrats wanted to support him.

It shouldn't have been. The turnout trend for Democrats in 2018 is not left-wing — it's universal. Delaware is just the latest state where the chance to cast a vote, any vote, pulled out Democrats who are angered and energized by the Trump administration. Carper's campaign, which always took the primary seriously, targeted and turned out more voters than it needed.

"I thought it would increase 50 percent over recent primary turnout — which was 30,000,” said Drew Serres, Harris's campaign manager. “It went two and a half times over that. And it’s cool for our state that so many people are getting involved."

Harris's campaign, which did not attract the same level of money as this year's successful insurgent efforts, might have boosted some Democrats down-ballot. Delaware, which has not elected a Republican to a major statewide office since 2008, is now a reliably blue state in presidential elections. But like many blue states — Rhode Island, New Jersey, Massachusetts — a conservative wing of the party holds the balance of power. Liberal reform goals such as early voting, prison reform and marijuana legalization are often smothered by a conservative bloc in Dover.

But the voter surge shook up some of the legislative races. In Delaware House District 1, Wilmington City Council member Nnamdi Chukwuocha ousted Rep. Charles Potter, who had been damaged by scandal; in District 17, Melissa Minor-Brown, a nurse who had never run for office, won a landslide victory for an open seat.

Serres was adamant that the credit for any upsets belonged to the candidates themselves. But Harris's campaign was the first serious left-wing effort the state had seen in years; it trained hundreds of volunteers, some of whom did double-duty, working for local liberal candidates they found once they plunged into politics.

What did any of it mean for Republicans? The party, which is defending the state treasurer's and auditor's offices, was outvoted across most of the state; in 33 of Delaware's 41 House districts, Democrats cast more votes. While the GOP is optimistic about reelecting State Treasurer Ken Simpler, it doesn't have a real opening in the Senate and House races; Carper's GOP rival, Rob Arlett, had just $14,544 left to spend as of mid-August, and House nominee Scott Walker was an unknown who did not file an Federal Election Commission report.

A weak Republican performance in November could, in the long run, strengthen the forces that backed Harris. While they wanted victory in 2018, one of their goals was to prove to Delaware Democrats such as U.S. Sen. Christopher A. Coons — 17 years younger than Carper and a rising centrist leader in the party — that they had a left flank to worry about.

The strongest left-wing candidacies in the 2018 cycle have come in places where there is no credible threat of a Democratic defeat, like in Ocasio-Cortez's Bronx or in Ayanna Pressley's Boston. Harris, who impressed Democrats on the trail, might be the start of a party-crashing wave.

"A lot of the people who voted for Carper hadn’t even heard of Kerri,” Serres said. “If we can get the word out on these future candidates, they have a good shot."