New Jersey moved a step closer last week toward overhauling its unique-in-the-nation election ballots, in a decision that could reshape party politics in the state for years to come.
But not — at least not immediately — for both major parties.
On Saturday, the federal judge who ordered the redesign, in response to a lawsuit filed in February by three Democratic candidates, said in a statement that only the Democratic primary, which includes the race to replace Senator Robert Menendez, would have to use the new ballot. The Republican ballot, he wrote, can stay the same, though he said his order did not prohibit Republican leaders from choosing to alter their party’s ballot.
The clarification is the latest twist in a long legal battle in New Jersey to shift the balance of electoral power away from party-backed candidates and open the door for newcomers in both parties. But if the decision stands, Republicans, too, may soon be forced to change their ballot, though perhaps not in time for the June 4 primary, said Julia Sass Rubin, a professor of public policy at Rutgers University who was an expert witness in the lawsuit.
“It’s just a hiccup,” Dr. Rubin said. “If this decision holds, it will completely upend New Jersey politics.”
On Friday, the federal judge, Zahid N. Quraishi of U.S. District Court for the District of New Jersey, ruled in favor of changing the format of primary election ballots used in 19 of 21 counties in New Jersey, which have historically favored candidates put forward by party bosses.
The so-called county-line ballot, in which local political leaders’ preferred candidates are grouped together in a prominent position, is an anomaly in the United States, with only New Jersey using the system, said Nicholas Stephanopoulos, a professor at Harvard Law School.
Representative Andy Kim, a Democrat who is running for Mr. Menendez’s Senate seat, had argued that he remained an underdog in the race, despite his rising standing in polls, because party officials backed the candidacy of Tammy Murphy, the wife of Gov. Philip D. Murphy. Mr. Kim and two other Democratic congressional candidates filed the February lawsuit to push for the ballot redesign.
A spokesman for Mr. Kim declined to comment on Sunday.
Mr. Menendez, who faces charges that include conspiring to accept bribes, obstruction of justice and plotting to act as a foreign agent, said earlier this month that he would not run for re-election as a Democrat this year. Ms. Murphy recently dropped out of the Democratic primary.
Although the judge’s decision affects only Democratic primaries, some Republican candidates who could benefit from the ballot revision are also agitating for change.
Christine Serrano Glassner, a candidate in the Republican Senate primary who supports former President Donald J. Trump, said in a statement on Friday that she supports eliminating the current ballot system.
“The county lines are now irrelevant, and the playing field has been leveled for a pro-Trump, grass-roots-supported candidate,” she said.
A spokeswoman for her Republican opponent, Curtis Bashaw, could not be reached.
Several county clerks are planning to appeal the decision to revise the ballots, but the time frame to do so is short. The federal deadline to send out ballots for overseas and military voters is April 20, according to Yael Bromberg, a lawyer representing the plaintiffs in the case.
Rajiv D. Parikh, a lawyer who represents county clerks who may appeal the decision, declined to comment.
But as of Sunday, two of the 19 counties that use the county-line ballots had said they would not appeal the judge’s decision, and others are expected to comply with the order, Ms. Bromberg said.
