A former U.S. attorney general who served under Democratic President Barack Obama joined a long list of critics Thursday warning against a controversial New Jersey redistricting plan that many say could allow Democrats to cement their control of the state Legislature for decades.

Eric Holder, a possible 2020 Democratic presidential candidate, released a statement opposing the proposal that Democratic state lawmakers are rushing to pass before the end of the year.

His remarks arrived just as a pair of simultaneous public hearings kicked off at the Statehouse in Trenton in which dozens of the opponents slammed the plan and only the measure’s sponsors spoke in favor of it during the 2 1/2 hours of testimony.

The proposal, if approved by the Democrat-led Legislature, would ask New Jersey voters next November to approve an amendment to the state constitution that would overhaul how the Garden State draws its legislative districts. Those are the areas represented by the elected members of the Legislature, the body that makes New Jersey’s laws and passes the state budget.

Critics — which include Republicans, Democrats, advocates, and academics — say the problem is the amendment would insert a new formula into the constitution that would heavily favor the Democratic Party. And one fear among Democrats is that could undermine the national party’s efforts to fight Republican gerrymandering in other states.

Holder now leads the National Democratic Redistricting Committee, a political group that battles gerrymandering, which is rigging an electoral map to benefit one party over another.

“As we’ve seen in states around the country this year, the American people want redistricting reforms that help level the playing field so that elections are decided on who has the best ideas, not which party was in charge of drawing the lines," Holder said in his statement, first published by the New York Times on Thursday morning.

“Any proposed reforms should put the interests of the people ahead of politicians and improve the current redistricting process in each state,” he added. “As currently constructed, the proposal in New Jersey fails to live up to those standards."

But sponsors vehemently defended the plan at Thursday’s hearings.

State Sen. Nicholas Scutari, a main sponsor, argued there’s been too much “hysteria” from people who don’t understand the proposal (SCR152/ACR205).

Scutari, D-Union, said it aims to make the process of choosing state lawmakers fairer and more reflective of New Jersey’s voters. Plus, he argued, those voters will have the final say.

“I’ve heard these outlandish reactions throwing around the word ‘gerrymandering,’" Scutari said. “It’s just simply not true. Just read the legislation that’s written.”

Top Democratic lawmakers said they’re still planning for both the state Senate and Assembly to vote on the proposal Monday, the final voting session of the year.

Under the state constitution, Democrats either need to pass the plan by simple majorities in two consecutive years, or by a three-fifths majority in one year.

Because the latter seems unlikely, a Monday vote is necessary for the plan to advance. Lawmakers could then vote again early next year.

But it remains unclear if Democrats have enough votes to pass it. A legislative source who spoke on the condition of anonymity told NJ Advance Media they’re very close.

The proposal has united usually warring factions. Republicans, who could see their minorities in the Legislature shrink even further, are fiercely opposed. Good-government groups are, too.

And Holder isn’t the only Democrat against it. So are Gov. Phil Murphy and left-leaning groups that typically back Democratic candidates. They say it’s a sneaky power grab that undercuts democracy, could disenfranchise voters of color, and is being rushed through during the holiday season.

The plan’s most controversial part would require at least 10 of the Legislature’s 40 districts be within five percent of the statewide party average in statewide elections — for president, U.S. Senate, and governor — the last 10 years. Sponsors say that’s an attempt to help make at least one-quarter of the districts competitive.

But that would likely benefit Democrats because the state has about 900,000 more registered Democrats than Republicans, hasn’t elected a Republican to the U.S. Senate since 1972, and hasn’t gone to a Republican presidential candidate since 1988.

The proposal would also change the makeup of the commission that draws the map. Currently, the state’s Democratic and Republican party chairs each chooses five members, and the state Supreme Court justice chooses the final member.

Under this plan, the party chairs and the four leaders of the Legislature would each get two picks apiece, and the justice would get the last one. Lawmakers would be required to be part of the commission, and two members of the public representing that state’s “ethnic, gender and racial diversity” would also have to be included — which Scutari said is a first.

“To me, I don’t see how people could be opposed to that,” the senator said.

But critics see the change as a way to curtail Murphy’s power because he’s aligned with Democratic State Party Chairman John Currie. Both Murphy and Currie sometimes clash with Democratic legislative leaders.

Among opponents' other complaints Thursday was that the hearings themselves — mandated by the state constitution — seemed designed to suppress criticism.

They took place at the same time in two different parts of the Statehouse, forcing some people to rush up and down elevators or stairwells to speak at both.

Meredith Meisenheimer of the advocacy group South Jersey Women for Progressive Change testified Thursday that she’s shocked the plan is being considered when Democratic voters are trending more progressive.

“They are watching what you do,” Meisenheimer said. “They want us to go forward. They do not want us to go backwards.”

Dueling public hearings on a controversial redistricting plan that could cement Democrats’ control of the N.J. Legislature have begun at the Statehouse in Trenton. Both are being held at the same time despite the outcry over the proposal. Background: https://t.co/4K8FaDY6iw pic.twitter.com/B9ArrHewLl — Brent Johnson (@johnsb01) December 13, 2018

We're close to 90 minutes into hearings on NJ redistricting and there hasn't been a single testimony in favor of the bill, save for the sponsor.



And aside from a Republican lawmaker, every oppositional testimony has been from nonpartisan or progressive groups. pic.twitter.com/4wcJlajUp8 — Nick Corasaniti (@NYTnickc) December 13, 2018

State Senate Minority Leader Tom Kean Jr., R-Union, called the proposal “a shameless stunt.”

“New Jerseyans will be left with little more than an illusion of choice when they enter the voting booth in future legislative elections," Kean said.

But Scutari, the main sponsor, argued the current legislative map — drawn in 2011 — is based on many ideas included in this amendment. This, he said, simply codifies it.

Scutari also said basing the changes on statewide elections make sense because “that’s a true reflection of who lives here in New Jersey.”

After the hearings, Scutari said he wasn’t discouraged mostly opponents showed up. He said he knows many supporters “that didn’t testify.”

State Assembly Majority Leader Lou Greenwald, another sponsor, argued that recent statewide elections have pushed New Jersey in a more Democratic direction. But Greenwald, D-Camden, said Republicans could regain power in the future, and this plan could then cause Democrats to lose seats.

“This amendment is about fairness and ensuring that the rules of engagement in redistricting are clear and will not be violated by personal or political agendas,” Greenwald said.

State Senate President Stephen Sweeney, another sponsor, dismissed Holder’s criticisms.

“I don’t agree with Eric Holder,” Sweeney, D-Gloucester, said. “I think it brings rules to the system. ... Otherwise, you can just create whatever map you want."

The governor has no power to block constitutional amendments from getting to the ballot if lawmakers act.

But Murphy told the New York Times that if it does pass, he will “fight it right through to the ballot box” next year.

“And you should assume that we ain’t giving up this fight,” he told the newspaper.

NJ Advance Media staff writer Matt Arco contributed to this report.

Brent Johnson may be reached at bjohnson@njadvancemedia.com. Follow him on Twitter @johnsb01. Find NJ.com Politics on Facebook.