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TRENTON — Legislative power brokers across the country have long designed district lines in back-room deals that entrenched their control for years, if not decades. But now, Democratic lawmakers in New Jersey are carrying out a power grab in an unusually public fashion: They are seeking to make Republicans a permanent minority by essentially writing gerrymandering into the State Constitution.

The New Jersey plan comes amid a national reckoning over the consequences of gerrymandering and has been met by fierce opposition across the political landscape — and not just from Republicans and nonpartisan watchdog groups.

Even some national Democratic leaders have criticized the plan, fearing that it undercuts Democratic efforts to attack what they term Republican strong-arm tactics in state capitals across the country. Republicans in Wisconsin and Michigan are facing an intense backlash after state legislatures there voted to strip power from newly elected Democratic governors.

Republicans have also come under fire for legislative gerrymandering in states like North Carolina.

Eric H. Holder Jr., a former attorney general under President Barack Obama and a potential presidential candidate in 2020, called on the Democratic lawmakers in the New Jersey Legislature, who have significant majorities in both chambers, to rethink their plan.