Josh Turek, a Paralympic gold medalist and state legislator, won the Democratic primary for U.S. Senate in Iowa on Tuesday, according to The Associated Press, defeating a progressive rival to capture the nomination in a contest that tested the party’s anti-establishment fervor.

Mr. Turek beat Zach Wahls, another state legislator, who rose to national attention in 2011 with a three-minute speech he made as a teenager at the Iowa Capitol defending his lesbian parents.

Running as a self-described “prairie populist,” Mr. Turek, 47, cast himself as a “battle-tested” candidate who could win the support of independents and Republicans in a state President Trump won three times.

“I outperformed the top of the ticket by Trump by 50 percent, more than any other Democrat in the state,” Mr. Turek said at a debate last month. “I know what it takes to win.”

He will face Representative Ashley Hinson, a congresswoman who represents the northwest corner of the state. The Senate Leadership Fund, the main super PAC for Senate Republicans, has already committed at least $29 million to backing her campaign, an early signal that the contest could be more competitive this year than in recent elections.

Democrats feel increasingly optimistic about their chances in Iowa, where Republicans control the entire congressional delegation, the governor’s mansion and both chambers of the state legislature.

Many national Democrats saw Mr. Turek, who won twice in a conservative-leaning statehouse district, as the stronger contender. He won the endorsement of former Senator Tom Harkin of Iowa — the architect of the Americans With Disabilities Act — and the last Democrat to hold the seat.

His campaign was helped by about $10 million in ads from VoteVets, a Democratic organization that typically backs veterans. Mr. Turek did not serve, but he was born with spina bifida after his father was exposed to Agent Orange in Vietnam. Mr. Turek, who campaigned across the state in his wheelchair, has said he endured 21 surgeries by the age of 12.

Mr. Wahls, 34, represents one of the bluest districts in the state. He attempted to transform the race into a proxy battle over frustrations with national Democratic leadership and a desire for generational change.

He promised not to vote for Senator Chuck Schumer of New York as caucus leader and called for the replacement of Ken Martin, the chairman of the Democratic National Committee.

Mr. Wahls characterized Mr. Turek as an extension of Mr. Schumer, who has frustrated many in the party’s grass roots with what they see as a reluctance to embrace new leaders and a willingness to accommodate the Trump administration. Mr. Schumer did not formally endorse Mr. Turek’s campaign, although a leadership PAC aligned with him made a donation.

“We need new leadership top to bottom,” Mr. Wahls said in an interview last month. “It’s just time to burn it all down and start over.”

Mr. Turek, who referred to himself as a “poor, disabled kid from Council Bluffs,” insisted he was not part of any party elite.

“I’m not a D.C. insider,” he said at a debate last month. “I don’t know these folks.”

Two other candidates who initially entered the race, J.D. Scholten and Nathan Sage, both dropped out and endorsed Mr. Turek.

Senator Joni Ernst, a Republican, in September opted out of running for a third term amid falling job approval ratings as she struggled to sell Mr. Trump’s domestic agenda. Her exit from the contest opened the seat for the first time since she replaced Mr. Harkin, who did not run for re-election in 2014.

Iowa, a state whose economy is heavily reliant on farming, has been struggling under the weight of Mr. Trump’s economic policies and war in Iran. The barrage of tariffs last year increased the cost of machinery and materials that many Iowan farmers rely on. And the ongoing war with Iran raised the cost of gas and drove Iowa fertilizer prices to near-historic highs.

Since Mr. Trump took office, Democrats have won two special elections for State Senate seats in conservative-leaning districts, raising hopes that the party could take those victories to statewide races.

The party has an unusual number of competitive races this year, with Gov. Kim Reynolds not seeking re-election and Democrats contesting three of the state’s four Republican-controlled House seats.