The U.S. Supreme Court and a federal district court on Monday declined requests by Pennsylvania Republicans to block a new congressional map issued by the state's high court last month.

Why it matters: The rulings comes amidst redistricting battles in key states over voting maps drawn after the 2010 census. Both Democrats and Republicans have legally designed maps to gain electoral advantages and capture majorities. These legal challenges could alter how lines are redrawn and set legal precedent for determining when redistricting is infected with political bias and racial discrimination.

As the 2020 census count looms — which lawmakers use to draw proportional electoral district lines every ten years — these cases could also affect the next round of redistricting and upend the control of Congress and state legislatures over the next decade.

Wisconsin

The latest: The U.S. Supreme Court is expected to rule on the case this spring.

The backdrop: Wisconsin Republicans appealed a lower-court ruling that struck down the legislative map drawn in 2011 citing that it was unconstitutional because it's heavily skewed in their favor. The court later ordered the state to draw a new map by Nov. 2017, a request the U.S. Supreme Court blocked when it agreed to hear the case last year.

Wisconsin Republicans appealed a lower-court ruling that struck down the legislative map drawn in 2011 citing that it was unconstitutional because it's heavily skewed in their favor. The court later ordered the state to draw a new map by Nov. 2017, a request the U.S. Supreme Court blocked when it agreed to hear the case last year. Why it matters: If the justices uphold a lower court ruling challenging the State Assembly Districts, this would be the first time the Supreme Court strikes down a voting map on the grounds of partisan gerrymandering.

Maryland

The latest: ​The Supreme Court will hear oral arguments in a partisan gerrymandering case on March 28. A decision is expected by June.

The backdrop: The case centers on the 6th congressional district, which was redrawn in 2011 to include parts of the heavily Democratic Montgomery County. ​While Republican voters argue that the Democratic-controlled legislature is unfairly drawn, three judges ruled against the plaintiffs' request to discontinue the use of the current map ahead of the 2018 midterm election.

The case centers on the 6th congressional district, which was redrawn in 2011 to include parts of the heavily Democratic Montgomery County. ​While Republican voters argue that the Democratic-controlled legislature is unfairly drawn, three judges ruled against the plaintiffs' request to discontinue the use of the current map ahead of the 2018 midterm election. Why it matters: ​This is the only redistricting legal battle filed against Democrats. Republicans there said the current map has diluted their votes and cost an incumbent his seat.​

Texas

The latest: The U.S. Supreme Court agreed in January to hear a racially-charged gerrymandering case sometime this spring, with a decision likely by June.

The backdrop: Two congressional and eight state legislative districts were ruled unconstitutional racial gerrymanders after a court said they violated the Voting Rights Act because lawmakers intentionally designed them to dilute the political power of minority voters who favor Democrats. Last year, the Supreme Court blocked a redrawing order for new maps ahead of this year's midterm as they consider an appeal from the state.

Two congressional and eight state legislative districts were ruled unconstitutional racial gerrymanders after a court said they violated the Voting Rights Act because lawmakers intentionally designed them to dilute the political power of minority voters who favor Democrats. Last year, the Supreme Court blocked a redrawing order for new maps ahead of this year's midterm as they consider an appeal from the state. Why it matters: This is a short-term victory for Republicans who appealed a lower court ruling that ordered them to draw new maps to remedy the alleged infractions ahead of this year's midterm election.

Pennsylvania

The latest: The U.S. Supreme Court and a federal district court on Monday declined requests by Pennsylvania Republicans to block a new congressional map issued by the state's high court last month. The rulings come amid concerns by GOP that the Pennsylvania Supreme Court overstepped its authority when issuing the map.

The backdrop: The nation's high court had rejected a similar request last month to block the ordering of a new map, after the state Supreme Court gave lawmakers and Gov. Tom Wolf (D) more than three weeks to agree on one, which they failed to do.

Why it matters: Early analysis of the new districts said elections will be more competitive and it would likely put several Republican-held seats in play for Democrats. Democrats who are hoping to defeat Republican incumbents in this year’s midterm elections and take control of the House.

In the meantime, Republicans have been considering impeaching the Supreme Court justices who struck down the gerrymandered map.

North Carolina

The latest: The U.S. Supreme Court in January issued a temporary hold on ordering the state legislature to redraw its excessively partisan congressional map.

Why it matters: This is a short-term victory for Republicans who hold 10 of the 13 U.S. House seats there. The high court did not say when the case would be resolved, but constitutional law expert and University of Richmond law professor, Carl Tobias, told Axios that the ruling issued in the Wisconsin case could be use to determine the North Carolina challenge after an appealed is filed.

Virginia

The latest: The Virginia Supreme Court is reviewing a racially-charged case regarding the 2011 redrawing of the states' House of Delegates district lines.

The backdrop: The U.S. Supreme Court told the lower court in March of last year that it must be reexamined for racial bias.

The U.S. Supreme Court told the lower court in March of last year that it must be reexamined for racial bias. Why it matters: The case centers on concerns that the map, drawn by Virginia's Republican-led legislature, had deliberately packed black voters together to limit their influence so surrounding districts could be more winnable for GOP lawmakers.

Michigan

The latest: ​A federal court will hear oral arguments on March 20 that seek to toss out the current legislative and congressional maps crafted by state Republicans.