Representative Andy Kim, a lawmaker who has turned New Jersey politics on its head since entering the race to unseat Senator Robert Menendez, won the Democratic nomination for Senate on Tuesday after a campaign marked by a watershed ballot-access ruling.
The victory makes Mr. Kim, 41, a favorite to become New Jersey’s next senator. He would be the first Korean American to be elected to the U.S. Senate.
The results capped a tumultuous campaign that began a day after Mr. Menendez, a Democrat, was accused in September of being at the center of a sprawling international bribery scheme. Mr. Menendez, a third-term senator who for decades shrewdly navigated New Jersey’s notoriously rough-and-tumble politics, did not compete for the Democratic nomination.
For months, Mr. Kim’s main opponent had been Tammy Murphy, the wife of Gov. Philip D. Murphy. Ms. Murphy, a first-time candidate, was bombarded by accusations of nepotism and dropped out of the race in March after failing to connect with voters.
Mr. Kim, a former member of the National Security Council who advised President Barack Obama on Iraq, was first elected to Congress in 2018 — one of four Democrats that year to flip a New Jersey district from red to blue after Donald J. Trump was elected president.
His victory on Tuesday came as Mr. Menendez was in his fourth week of a federal trial in Manhattan, defending himself against some of the most serious charges ever leveled against a sitting member of Congress.
Mr. Menendez, 70, has refused to resign, and on Monday he took steps to have his name imprinted on a ballot at least one more time by filing to run for re-election in November as an independent.
Voters said Tuesday that they were skeptical he had any political future at all.
“He’s done for — he’s not going to win anything,” June Ackermann, 67, a nurse from Freehold, N.J., said. She said she had cast her ballot before Tuesday, during the early voting window, in part because politics had “gone upside-down crazy.”
Mr. Kim’s victory came as ballots were also cast in primary elections for president and 11 of the state’s 12 seats in Congress. (A special election will be held in September for the House seat once held by Representative Donald M. Payne Jr. of Newark, who died in April.)
Many of the races were directly affected by Senator Menendez’s legal trouble, as well as a court decision that changed the rules governing how Democratic candidates would be listed on the state’s primary ballots.
The senator’s criminal case thrust his son, Representative Rob Menendez, 38, into a suddenly competitive race for re-election. The younger Menendez has spent months trying to avoid becoming one of the biggest casualties of his father’s corruption trial and fending off accusations by his main opponent, Ravi Bhalla, the mayor of Hoboken, N.J., that he represented the same broken machine politics that his father has come to embody.
Mr. Kim’s margin of victory was sizable. With just over 20 percent of the votes tallied shortly after polls closed on Tuesday, he had more than 80 percent of the vote, according to The Associated Press. He beat two left-leaning Democrats, Larry Hamm and Patricia Campos-Medina.
Curtis Bashaw, a hotel developer from Cape May, N.J., and Christine Serrano Glassner, the mayor of Mendham Borough, N.J., were among the Republicans competing to run for U.S. Senate. Mr. Bashaw, 64, is a political moderate who has expressed support for Mr. Trump, who continues to hold sway over the Republican base in left-leaning New Jersey.
But the former president awarded his endorsement to Ms. Serrano Glassner, 60, during a well-attended beachfront rally in Wildwood, on the Jersey Shore. Ms. Serrano Glassner, whose husband has done political work for Mr. Trump, said during a debate that she would have voted against certifying the 2020 election results.
Whoever wins the Republican primary will face a tough race against Mr. Kim in November.
It has been 52 years since New Jersey voters elected a Republican senator; Democrats hold a 930,000-person registration advantage, and Mr. Trump lost to President Biden in New Jersey by 16 percentage points in 2020.
Senator Menendez’s entry into November’s race as an independent has the potential to offer Republicans a boost, however, by fracturing the Democratic vote. Mike Berg, a spokesman for the Republicans’ national campaign operation, said Monday that the party was “keeping a close eye on New Jersey.”
The senator’s reasons for running may have little to do with re-election. By remaining in the race, Mr. Menendez can continue to collect campaign contributions to supplement the $3.5 million he had on hand as of last month. He has already spent more than $3 million on his current team of lawyers, and the trial is expected to last for at least another four weeks.
The senator is also using his campaign account to pay lawyers representing his wife, Nadine Menendez, who is also charged in the bribery conspiracy and is expected to stand trial this summer.
Mr. Kim’s decision to run for the Senate meant that, win or lose, he would have to vacate his House seat in a South Jersey district redrawn after the 2020 census to favor Democrats.
Two prominent Democratic candidates quickly emerged, both State Assembly members: Carol Murphy, 61; and Herb Conaway, also 61.
Mr. Conaway, a physician who also has a law degree and was first elected in 1997, was endorsed by several Democratic county organizations. In past years, that would have afforded him a prominent spot on the ballot, known as “the county line,” and would most likely have been enough to propel him to Congress.
But a legal challenge Mr. Kim filed in February has fundamentally reshaped electoral politics in New Jersey, and the race for his replacement is likely to offer the first clear test of the new rules.
Siding with Mr. Kim, a judge ordered Democrats to stop grouping all candidates endorsed by the county political party in a single line on the ballot and to instead present the names of candidates running for each office together.
That’s the way it is done in every other state, but the shift was expected to be a wild card in several close elections on Tuesday in New Jersey, including Representative Menendez’s.
Representative Menendez was elected to a first term in 2022. He had never held office before then but was able to clear the field on the strength of his father’s connections — even before he announced he was running.
This election, the political landscape was far different. After Senator Menendez was indicted last year, Mr. Bhalla, the first Sikh to lead a New Jersey city, jumped into the House race. He has emphasized Representative Menendez’s connections to his father and outpaced the congressman in fund-raising.
Representative Menendez won the endorsements of the state’s leading Democrats, including the governor, who brought with them a well-oiled party apparatus skilled at getting out the vote.
Mr. Bhalla, 50, filed a legal brief in support of Mr. Kim’s lawsuit to end the county line. And the altered ballot design was expected to play a role in the race for the Eighth Congressional District.
“It makes both candidates work harder,” Mr. Bhalla, a civil rights lawyer, said last month at a forum in Jersey City, N.J.
Elise Young contributed reporting.