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 are just some pending redistricting lawsuits:

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.

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.

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.

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.

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.