FLEMINGTON, N.J. – U.S. Rep. Andy Kim (D-N.J.) won the endorsement of the Hunterdon County Democratic Committee for his Senate campaign on Sunday, but not before a bit of party insider hijinks threatened to derail proceedings with allegations of favoritism toward Kim’s chief rival, New Jersey first lady Tammy Murphy.

The endorsements of county parties are highly sought after in New Jersey because of the Garden State’s unique insider system, where county party endorsements determine who gets the coveted “ballot line” in a party primary. Getting “the line,” as it’s known, means that voters see the candidate’s name first on the ballot — an advantage for candidates among lower-information voters in particular.

Going into the Hunterdon County Democratic Committee’s convention vote on Sunday, Kim was the oddsmakers’ favorite to pick up the county party’s endorsement over Murphy. Kim, Murphy, labor activist Dr. Patricia Campos-Medina and civil rights advocate Larry Hamm are all vying for the chance to unseat federally indicted Sen. Robert Menendez in New Jersey’s June primary.

Before the 189 delegates present at the convention had a chance to cast their secret ballots, however, Arlene Quiñones Perez, chair of the Hunterdon County Democratic Committee, announced that any candidate who reached the 30% threshold would be able to qualify for “the line.” The announcement was met with loud boos from the crowd’s many Kim supporters.

Quiñones Perez framed the decision as an effort to heed Kim, Hamm and Campos-Medina’s calls to get rid of the county ballot line system altogether.

“We have … heard from the Senate candidates that they want an open primary,” Quiñones Perez said. “And we’ve heard from a great many of you that you want the same thing.”

“If you meet 30%, we think that is a reasonable number,” she added by way of explaining the threshold.

In fact, Kim, Campos-Medina and Hamm’s letter to county party chairs earlier this month called for the chairs to contact their county clerk and state legislators and request an “office block ballot arrangement for all competitive elections in this primary.” In other words, a ballot where no candidate gets a preferential “line.”

The candidates made it clear though that they saw this as an advocacy effort to remove favoritism across the state, not to unilaterally decide that within each county Democratic Party’s contest.

“We reaffirm our previously stated commitment and support for an office block ballot statewide, irrespective of the outcomes of any upcoming county conventions and ask you to do the same,” the candidates wrote in the letter.

Amid the howling over Quiñones Perez’s proposal, she offered the assembled convention delegates the opportunity to appeal her decision, which they promptly did by voice vote.

Kim received 62% of the vote, Murphy 33% and Campos-Medina 5%. And since the rule did not change, Kim will get exclusive access to the ballot line.

Speaking to reporters after the vote, Kim called the attempt at a last-minute rule change “insane.”

He noted that their proposal was not even for a countywide “office block ballot,” because it did not grant parity for all candidates regardless of their performance at the county party convention.

Kim suggested that those rules were designed to benefit Murphy.

“They were trying for a shared ballot to have a threshold that seems suspiciously close to what the final count would have been to make a difference,” he said.

Quiñones Perez has ties to Murphy and her husband, New Jersey Gov. Phil Murphy (D), that support the idea that she was trying to put her thumb on the scale for Tammy Murphy. Quiñones Perez was among a select group of county party chairs that the Murphys convened to talk strategy two weeks ago after Tammy Murphy lost the Democratic endorsement in Monmouth County where she lives, according to the New Jersey Globe.

“I bet the First Lady will probably gather a bunch of chairs at her house again after this weekend to try to figure out what comes next for them,” Kim joked on Sunday. “But whatever they’ve tried hasn’t worked.

Kim has accused Murphy of leveraging her husband’s power to cut deals with party power brokers to advance her candidacy.

After the vote on Sunday, Murphy denied that she had pushed for the rule change but conceded that she had heard about it prior and spoke positively about Quiñones Perez’s rationale for making it.

“They were trying to find an equitable way to be responsible,” she said. “And I don’t know, I thought it actually might have made sense, but I don’t know.”

Getting “the line” in Hunterdon County, a largely rural, Republican-leaning county with about 130,000 residents, is not exactly a game-changer for Kim. Earlier this month, Murphy locked up “the line” in far more populous Passaic County, where the county party endorsed her following a closed candidate screening rather than a convention.

In the coming weeks, Murphy is also favored to win the endorsements of the county parties in the major, Democratic-leaning population hubs in central and North Jersey. The chairs of the Essex, Bergen, Hudson, and Middlesex County parties, many of whom profit individually from their business before Gov. Murphy, endorsed Tammy Murphy shortly after she announced her candidacy in November. EMILY’s List, which backs pro-choice women candidates, and major labor unions have since followed suit.

But the Hunterdon County endorsement is Kim’s third consecutive pickup, following the closely fought bid for the Monmouth County endorsement on Feb. 10, and a homefield romp in Burlington County this past Saturday. (Kim lives in Burlington County and represents it in Congress.)

Those losses have shaken up Murphy’s campaign because her path to the nomination always ran through insider support in general, and county party endorsements in particular.

Perhaps in response to Kim’s perceived momentum – he is also leading Murphy by 12 percentage points among likely Democratic primary voters, according to a Fairleigh Dickinson University poll at the start of the month – the Murphy campaign parted ways with its campaign manager last week.

On Sunday, Murphy tried to draw attention to her achievements as First Lady, such as her work leading a program to reduce maternal mortality.

“We need more ticked off mothers in Washington, D.C., who are beholden only to the children!” Murphy declared in her speech to the convention. “We need a senator who will be a champion for our women and girls, and stop the right-wing extremists from banning abortion in all 50 states!”

But the Hunterdon County Democratic Committee’s decision to spring a new proposal for ballot line rules invariably made New Jersey’s clubby, machine politics – and Murphy’s role in them – a focus for many Kim supporters at the convention.

Jennifer Robinson, a Tewksbury retiree supporting Kim, felt more committed to Kim following the convention dustup.

“Andy Kim is a straight arrow and we are trying to replace Menendez. None of us trusted him,” she said. “We don’t want to go down that road again.”

Asked whether he wanted someone to run against Quiñones Perez for county chair, Jennifer’s husband, Steve Robinson, replied, “I hope someone does.”

Ken Short, a scientist from Tewksbury, lamented what he saw as the lack of notice that convention delegates had received about Quiñones Perez’s plans.

“I’m upset with the manner in which that motion was introduced,” Short said. “The logical conclusion would be that there was a recognition that Tammy is not going to get the majority and still have the party line.”

HuffPost asked Michael Drulis, a spokesperson for Quiñones Perez, why the county party had not informed the convention delegates of the rule change in advance.

“They were informed at that point,” he said. “The chairwoman gave the information and everyone in the room heard it.”