Republicans now control the White House and both houses of Congress, but the North Carolina ruling puts Republican congressional districts at risk in the 2018 election.
The U.S. Supreme Court last June upheld a lower court's ruling that Republican lawmakers in North Carolina had mapped state legislative districts in a way that diluted the clout of black voters.
Gerrymandering has drawn opposition from both sides of the political aisle.
The day before the judges' ruling in Philadelphia, a panel of federal judges in North Carolina ruled that state's congressional map unconstitutional and ordered the Legislature to redraw it this month.
The plaintiffs can appeal the decision to the U.S. Supreme Court.
For Mattingly, Tuesday's ruling was "an important step in the conversation" about the use of mathematics to illuminate such problems.
The judges agreed the current map violated the Equal Protection clauses of the Constitution. One notable feature of the district's border is how it snakes around the 4th District to the east.
The group of Democratic voters is planning to appeal the ruling.
Year-old Texas church massacre victim finally gets to go home
Ryland Ward, 6, a survivor of the Sutherland Springs church shooting, rides home in a fire department truck on January 11, 2018. Some members of the Sutherland Springs community welcomed Ryland home as he passed through town on the fire truck.
The deadline is important because candidates for the November congressional elections begin filing for the primaries on February 12.
A majority of the judges also agreed on January 9 they would hire a redistricting expert to draw replacement boundaries if the state legislature won't. "A gerrymander is by definition and common understanding a strange-looking monster drawing", North Carolina GOP Chairman Robin Hayes said in a statement. The city of Asheville saw the biggest change during the redistricting the court just rejected.
Osteen pointed to comments from Tom Hofeller, a go-to mapmaker for Republicans in North Carolina and other states, who acknowledged efforts "to minimize the number of districts in which Democrats would have an opportunity to elect a Democratic candidate".
If they can not agree, as the failed to in the Covington case, the court will appoint its own expert.
"T$3 he 2016 Plan's demonstrated partisan favoritism", the court concluded, "simply is not authorized by the Elections Clause".
Meanwhile, the ruling puts Republicans in a tight spot. Pennsylvania's Supreme Court will soon rule on whether the GOP unconstitutionally gerrymandered congressional districts in the Keystone State.
J. Michael Bitzer, a professor of political science at Catawba College near Charlotte, told The New York Times that new maps could give some political "hope" to Democrats in time for the midterm elections this year. But there's no question new maps would also leave candidates scrambling, especially Republican incumbents who previously won by less than comfortable margins and Democratic challengers with less name recognition.
"None of them emphasizes district shapes", he said. "You know, the people ought to pick their politicians".