Gerrymandering is on trial as the U.S. Supreme Court and judges in a dozen states consider whether mapmakers — typically state lawmakers — have gone too far in manipulating the boundaries of legislative districts for their own advantage.

The high court is to hear arguments Tuesday on a pair of cases alleging unconstitutional political gerrymandering. One claims Maryland Democrats gerrymandered a U.S. House district to defeat a Republican incumbent. The other claims North Carolina Republicans gerrymandered the state's congressional map to give their candidates a better chance of winning seats.

Earlier this week, the Supreme Court heard arguments on a separate case alleging unconstitutional racial gerrymandering in Virginia based on the way the Republican-led Legislature drew some of the state House districts.

The gerrymandering lawsuits challenge districts drawn based off 2010 Census data. They seek to force new district boundaries before the next legislative elections. But the cases also could set precedents for states to follow during the next round of mandatory redistricting that will occur after the 2020 Census.

Here's a state-by-state look at pending redistricting lawsuits:

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ALABAMA

The claim: Racial gerrymandering.

The case: A trial is scheduled for September on a federal lawsuit alleging the U.S. House maps approved in 2011 by the state's Republican-led Legislature and GOP governor illegally limit the voting influence of black residents. The lawsuit is backed by a national Democratic redistricting group.

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CONNECTICUT

The claim: Prison gerrymandering.

The case: A federal lawsuit filed last June by the NAACP alleges unconstitutional prison gerrymandering in the drawing of state House and Senate districts. It challenges the state's decision to count prisoners as residents of the district where they are incarcerated instead of their home districts. The lawsuit says prisoners are disproportionately black and Latino and from urban areas, but they are often placed in prisons in rural areas that otherwise are overwhelmingly white. The districts were drawn in 2011 by a bipartisan commission. No trial date has been set.

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GEORGIA

The claim: Racial gerrymandering.

The cases: A federal lawsuit filed last June and backed by a national Democratic redistricting group alleges that a U.S. House district was redrawn in 2011 by the state's Republican-led Legislature and GOP governor to illegally limit the voting influence of black residents. No trial date has been set.

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LOUISIANA

The claim: Racial gerrymandering.

The case: A federal lawsuit filed last June and backed by a national Democratic redistricting group alleges the U.S. House maps approved in 2011 illegally limit the voting influence of black residents by packing a large number into one majority-minority district and spreading other black voters out among multiple districts. Republicans controlled both legislative chambers and the governor's office at the time the redistricting plan was approved during a special legislative session. No trial date has been set.

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MARYLAND

The claim: Partisan gerrymandering.

The case: The U.S. Supreme Court is to hear arguments Tuesday on an appeal of a ruling that western Maryland's 6th Congressional District is an unconstitutional partisan gerrymander that diluted the voting power of Republicans. The district had been held by a 20-year Republican incumbent, but the Democratic governor and Democratic-controlled Legislature redrew it in 2011 to extend into suburban Washington, D.C. That added tens of thousands of Democratic voters while dropping Republican voters. Democrats have won the district in each election since then.

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MICHIGAN

The claim: Partisan gerrymandering.

The case: A federal court panel held a trial in February on a lawsuit by Democratic voters alleging that Michigan's U.S. House and state legislative districts are unconstitutionally gerrymandered to dilute the voting power of Democrats. The panel has not yet ruled on the lawsuit. Michigan's U.S. and state legislative districts were enacted in 2011 by a Republican governor and Republican-led Legislature.

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MISSISSIPPI

The claim: Racial gerrymandering.

The case: A federal judge ruled in February that one of Mississippi's 52 state Senate districts violates federal law because it doesn't give black voters an "equal opportunity" to elect a candidate of their choice. A federal appeals court panel has given the Republican-led state Legislature until April 3 to come up with new boundaries for Senate District 22, which was originally drawn in 2012. The deadline to qualify for this year's legislative primaries was March 1, but the appeals court panel said candidates can have until April 12 to qualify to run in any Senate district affected by the yet-to-be-finalized new map. Mississippi's legislative primaries are scheduled for Aug. 6

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NORTH CAROLINA

The claims: Partisan and racial gerrymandering.

The cases: The U.S. Supreme Court is to hear arguments Tuesday on an appeal of a federal court ruling that the Republican-led state legislature engaged in unconstitutional partisan gerrymandering when it redrew congressional districts in 2016. (Lawmakers were redrawing the districts in response to a previous court ruling that some 2011 districts were an unconstitutional racial gerrymander).

Separate lawsuits have challenged state House and Senate districts. A federal court ruled in 2016 that 28 state legislative districts were unconstitutional racial gerrymanders. The legislature redrew the districts the next year, and federal judges in early 2018 required additional changes. On Nov. 2, a state judicial panel struck down four of those redrawn House districts, ruling that it wasn't necessary to change them to comply with the earlier rulings. The legislature is to redraw those districts by this summer. Last November, the state Democratic Party and other plaintiffs filed a new lawsuit in state court contending the state's House and Senate districts are partisan gerrymanders that disadvantage Democratic voters in violation of the state constitution. A trial is scheduled for mid-July.

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OHIO

The claim: Partisan gerrymandering.

The case: A federal court panel held a trial earlier in March on a lawsuit by Democrats alleging that unconstitutional partisan gerrymandering has disadvantaged Democratic voters in Ohio's U.S. House districts. The panel has not yet ruled on the lawsuit. The current map was enacted in 2011 by a Republican governor and Republican-led Legislature.

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TEXAS

The claim: Racial gerrymandering.

The case: U.S. and state House maps enacted in 2011 by the Republican governor and GOP-led Legislature were tossed out in 2012 by a federal court, which produced new interim maps. Those maps were permanently adopted by the Legislature and governor in 2013. But in 2017, the federal court ruled that some districts were racially gerrymandered to weaken the electoral power of growing minority populations. The U.S. Supreme Court largely overturned that decision last June, striking down only one state House district in Fort Worth. A lower court deferred redrawing that district to allow time for the Legislature to do so during the 2019 session. But the Legislature has not approved new district boundaries, and the court now is considering alternative proposals submitted by the attorney general's office and by Latino and Mexican-American groups.

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VIRGINIA

The claim: Racial gerrymandering.

The case: The U.S. Supreme Court heard arguments Monday on claims of unconstitutional racial gerrymandering involving 11 Virginia state House districts. A lower court panel ruled last June that the Republican-led Legislature in 2011 had packed black voters into certain districts so that surrounding ones would have more white and Republican voters. In January, the federal court panel adopted a plan to redraw 26 legislative districts, including the 11 at issue and others adjacent to them, that would shift some districts toward Democrats. While the Supreme Court considers the case, the state is using the new court-ordered boundaries for candidates who are filing to run in the June 11 primary elections. The candidate filing period is schedule to run until March 28.

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WISCONSIN

The claim: Partisan gerrymandering.

The case: A new federal trial is scheduled to begin July 15 on a partisan gerrymandering lawsuit involving the state Assembly. It had been scheduled to start in April, but a federal court delayed the trial to allow time for the U.S. Supreme Court to rule on the North Carolina and Maryland cases, which could provide a precedent.

The U.S. Supreme Court in June 2018 overturned a November 2016 lower court ruling that had struck down Wisconsin's state Assembly districts as an unconstitutional partisan gerrymander. The lower court had said the map adopted in 2011 by the Republican-led Legislature and Republican governor violated Democratic voters' rights to representation by packing Democrats into some districts and spreading them among others, thus diluting their voting power. The U.S. Supreme Court said plaintiffs failed to prove they had the right to sue on a statewide basis. It sent the case back to the lower court for plaintiffs to attempt to prove that their personal voting rights were infringed by the way specific districts were drawn.

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