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JEFFERSON CITY, Mo. — Republican senators rolled out a plan Tuesday to ask Missouri voters to undo key parts of a nationally unique redistricting model that directs a demographer to draw new legislative districts with "partisan fairness" and "competitiveness" as top criteria.

The Republican proposal would abolish the demographer position and relegate political fairness and competitiveness to the bottom of the priority list, behind such criteria as compact and contiguous districts that keep communities intact.

"We’re going to provide voters with another option," Senate President Pro Tem Dave Schatz said.

Republicans currently hold commanding majorities in Missouri's House and Senate. An Associated Press analysis of Missouri's redistricting formula shows it is likely to lead to Democratic gains while dropping Republican majorities closer to the more even partisan division often reflected in statewide races.

During its first Senate committee hearing Tuesday, the GOP proposal drew opposition from supporters of the original ballot measure, called “Clean Missouri,” which was approved by voters by 62%.

The initiative “set it up so the system is not as politically influenced,” said John Madras, a Sierra Club member who said he circulated petitions to help get the Clean Missouri measure on the ballot. “This bill reverses that and returns it to an entirely political process.”

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If approved by the House and Senate, the newly proposed constitutional amendment would go before voters later this year, most likely during the November general election.

Missouri was one of five states where voters in 2018 approved redistricting ballot measures designed to decrease the potential for partisan gerrymandering when redrawing voting districts after the 2020 census. Missouri's measure was packaged with other popular ethics reforms that imposed a $5 limit on lobbyist gifts to lawmakers, lowered legislative campaign contribution limits and opened more legislative records to the public.

The new Republican proposal would present voters with more appealing ethics changes — banning lobbyist gifts entirely and lowering contribution limits even further for state senators. But its main purpose is to reverse portions of the redistricting model for state House and Senate seats.

Neither the 2018 measure nor the new Republican proposal affects redistricting for the U.S. House, which would continue to be passed as a bill by state lawmakers subject to a gubernatorial veto.

The Missouri Constitution says state House and Senate districts are to be approved by a pair of bipartisan commissions whose members are nominated by the Republican and Democratic parties and appointed by the governor. That has allowed consultants and experts hired by the parties to work behind the scenes to develop maps, though the current state House districts were drawn by a judicial panel after the bipartisan commission failed to agree on a plan.

The 2018 ballot initiative requires a new nonpartisan state demographer to submit redistricting plans to the bipartisan commissions based on the votes cast in the previous three elections for president, governor and U.S. senator — races that are decided by voters statewide and are not affected by gerrymandering. The districts must come as close as practical to achieving "partisan fairness" as measured by a formula called “the efficiency gap.”

The new Republican proposal scraps the involvement of the nonpartisan demographer, lowers the priority of partisan fairness and allows a 15% difference in the partisan fairness calculation, which is large enough that some districts could be gerrymandered for partisan purposes.

"The criteria that ensure fair maps are weakened or gutted,” said Sean Nicholson, campaign director for Clean Missouri.

Though Republicans said their proposal continues to make it a priority for districts to protect minority voting rights, Nicholson said the effect of its specific wording could diminish the ability of minorities to elect a candidate of their choosing in some districts.

Nicholson watched but did not testify at the Senate hearing. While it was underway, Clean Missouri sent out a fundraising email for a campaign to try to defeat the Republican proposal.

Republican Senate leaders said their proposal is intended to decrease the likelihood of communities being split among multiple districts in order to achieve goals for partisan fairness and competitiveness.

The proposal takes legislative redistricting “back to a similar process that we have used before — I would argue successfully — for decades,” said Sen. Dan Hegeman, the lead sponsor of the measure.