Bucking a national trend toward fighting gerrymandering by removing partisan politics from the process of drawing political maps, New Jersey Democrats are seeking to amend the state constitution in a way that would entrench their power in Trenton.

The proposal has drawn sharp criticism from good-government groups, civil rights groups, and redistricting experts who warn it would allow Democrats to unfairly draw the state's legislative districts in their favor. A group led by prominent national Democratic figures called it "a major step in the wrong direction."

Top Democratic lawmakers this month hope to quickly advance the proposal, which would increase their role in drawing the legislative maps and explicitly use the previous decade's election results in determining district boundaries for the next 10 years. Voters could be asked to weigh the amendment as early as next November.

While wrapped in the language of anti-gerrymandering redistricting reform, the proposed constitutional amendment largely ignores best practices and instead orders mapmakers to impose Democrats' advantage in statewide elections onto local legislative districts.

If enacted, the proposal would require mapmakers in 2021 to redraw the state's 40 districts in a way that would ensure no more than 15 would lean Republican.

And there's a twist: While fights over gerrymandering typically pit Democrats against Republicans, this proposal has also become the latest flash point between the state's top elected Democrats — Gov. Murphy and Senate President Steve Sweeney of Gloucester County.

The proposal is particularly striking because Democrats nationally have sought to position themselves as the party of good government, including opposing gerrymandering. Former President Barack Obama has personally focused on the issue. And a growing number of states have adopted redistricting reforms to minimize partisan politics in the mapmaking process.

"This is not how we achieve fair maps," Helen Kioukis, a staffer at the nonpartisan League of Women Voters of New Jersey, told lawmakers Monday. "When all other states are moving forward and improving this fundamental component of our democracy, New Jersey is moving backward with a proposal that's nothing more than a partisan gerrymandering bill."

A previous version of the amendment stalled when it was introduced three years ago. Democratic leaders hope to pass it in December and put it before voters next year, amending the state constitution before the 2021 redistricting round. To be placed on the ballot, both chambers would have to pass the bill with simple majorities in two consecutive years; otherwise, it would require three-fifths votes, which could be harder to muster.

Democratic lawmakers said the amendment would protect against gerrymandering by requiring mapmakers to take election results into account.

"It is not about a Republican or Democrat map," said Assembly Majority Leader Lou Greenwald (D., Camden). "It's about a map that would reflect, in a percentage, the will of the voters."

He predicted it would become a national model.

A number of nonpartisan good-government groups and redistricting experts disagree. At a committee hearing Monday, witnesses from the Brennan Center for Justice at New York University and the ACLU called for Democrats to reconsider their approach. The state chapter of the NAACP also opposes the measure.

The Center for American Progress, a liberal-leaning research group with strong ties to national Democrats, warned New Jersey Democrats to act differently from Republican lawmakers accused of gerrymandering other states. In Pennsylvania, for example, the state Supreme Court ordered congressional maps redrawn this year because they were so gerrymandered in the GOP's favor.

"The proposed constitutional amendment to New Jersey's redistricting process would be a major step in the wrong direction," the group said.

Republicans have denounced the New Jersey proposal as a dangerous power grab.

Some parts of it, such as increasing transparency and public input in the redistricting process, were welcomed by advocates. The criticism centers on two major changes: altering the composition of the redistricting commission and forcing mapmakers to draw districts based on partisanship.

The 40 legislative districts are redrawn once a decade by a 10-member commission, with the chairs of the state Democratic and Republican Parties appointing five members each. If the commission deadlocks, the chief justice of the New Jersey Supreme Court appoints an 11th member to break the tie and decide how the map will be drawn. (A separate commission draws the congressional map.)

The new plan calls for a 13-member commission. The party chairs would each appoint two, legislative leaders from both parties would appoint eight others, and the chief justice would select the 13th.

"The selection process is no longer going to be bound to just two party bosses," said State Sen. Nick Scutari (D., Union), who sponsored the proposal.

But transferring authority to legislative leaders would empower them to punish lawmakers who step out of line on key policy initiatives, said Analilia Mejia, executive director of New Jersey Working Families Alliance.

"I think it's a terrible idea," she said. Like others, she favors a commission with no lawmakers.

The effort to diminish the role of state party chairman John Currie, a Murphy ally, has added to the animosity between the governor and Sweeney, who have clashed over other initiatives. Murphy opposes the proposal.

Democrats also said the amendment would protect against the whims of mapmakers by requiring the map be drawn according to the outlined principles of "competitiveness," based on statewide election results over the previous decade.

It would consider all elections for governor, president, and U.S. Senate that occurred since the last redistricting round to determine an overall percentage of Democratic and Republican votes. At least 10 of the 40 new districts would be required to fall within 5 percentage points of that statewide number.

Although Republicans have won the governorship, no GOP presidential nominee has carried New Jersey in three decades, and the party hasn't won a Senate race in nearly a half-century.

This decade, Democrats have won about 55 percent of the vote in statewide elections. That means at least 10 of the districts must be drawn to fall within the range of 50 to 60 percent Democratic-leaning. None of those 10 (or more) would be Republican-leaning.

The remaining districts would be divided so half are more Democratic-leaning than that range and half are more Republican-leaning.

Thus, no more than 15 districts could be drawn to favor Republicans to any degree. And for every such district, a corresponding one is at least 60 percent Democratic.

But redistricting reform advocates generally seek to remove partisanship from the mapmaking process entirely — not to require it to be considered.

"To the extent that it's possible and politically feasible, it [redistricting] should be buffered from the political process," said Yurij Rudensky, a redistricting lawyer at the Brennan Center for Justice.

Where partisanship data should come into play, Rudensky said, is after a map is drawn, to test whether the map is unfairly skewed in one party's favor.

Experts and advocates also expressed concern about using the previous decade's results to draw maps for the next decade — why use Obama's 2012 win to draw lines for the 2029 legislative races? — and that voters vote differently in statewide elections from local ones.

The constitutional amendment would tie the hands of "every commission, forever," Monmouth University political analyst Patrick Murray said, and "create a gerrymander that in fact is the kind of thing that courts are overturning when you use this kind of political calculation."

Democrats tried to pass a similar amendment three years ago as part of a legislative package on voting rights and elections, including same-day voter registration and expanding early voting, but the measure stalled.

The revived proposal passed a committee vote on party lines Monday. Hearings on full Senate and Assembly votes have not yet been scheduled.