The Supreme Court on Monday denied a request from Pennsylvania Republicans to delay redrawing congressional lines, meaning the 2018 elections in the state will most likely be held in districts far more favorable to Democrats.

The Pennsylvania Supreme Court last month ruled that the state's Republican legislative leaders had violated the state Constitution by unfairly favoring the GOP. Although there are more registered Democrats than Republicans in the state, Republicans hold 13 of 18 congressional seats.

The GOP leaders asked the U.S. Supreme Court to intervene, but Justice Samuel A. Alito Jr. turned down their request for a stay without even referring the case to his colleagues. He gave no reason for the decision, but generally the Supreme Court stays out of the way when a state's highest court is interpreting its own state constitution.

The process of redrawing district lines to give an advantage to one party over another is called "gerrymandering." Here's how it works. (Daron Taylor/The Washington Post)

The practical impact is that it might aid Democrats in their attempt to flip the House from Republican control. Democrats need to take about two dozen seats to win the majority, and Pennsylvania could provide some of that total. Six incumbents, five of them Republicans, have said they will not be on the fall ballot.

The victory for opponents of partisan gerrymandering might also indicate a new way to combat the issue, by challenging redistricting in state courts under state constitutions.

Federal courts in Texas, North Carolina and Wisconsin found that politics or intentional discrimination played an unacceptable role in drawing electoral lines and ordered new districts drawn for the 2018 elections. But the Supreme Court stopped those decisions, and Monday's denial to Pennsylvania's request does not affect them.

The justices are traditionally reluctant to order changes in an election year. And they have never thrown out a state's redistricting plan because they found it so infected with partisan bias that it violates voters' constitutional rights.

Unless and until it does — the subject is under review at the high court in cases from Wisconsin and Maryland — the justices have routinely told states found to be offenders that they do not have to immediately redraw the maps.

But the previous decisions have been by federal courts weighing how gerrymandering might violate the U.S. Constitution. The Pennsylvania case was brought under the commonwealth's Constitution, and the U.S. Supreme Court generally does not interfere in such decisions.

"State courts long before this decade of redistricting have been somewhat more willing to strike down partisan gerrymanders than federal courts, though that isn't saying much, because federal courts have not been willing to do so at all," said Richard Pildes, an election law specialist at New York University Law School.

The Pennsylvania Supreme Court last month ruled that the congressional map drawn by the Republican legislature in 2011 "clearly, plainly and palpably violates" the commonwealth's Constitution. It demanded a quick redrawing of the lines so that 2018 elections could be held in fairer districts.

Pennsylvania's Supreme Court justices are elected and, with Democrats in the majority, voted along party lines in demanding a change to the districts.

Republican legislative leaders in Pennsylvania had asked the U.S. Supreme Court to put the decision on hold. And other Republican-led states told the justices that they should refrain from ordering new districts anywhere, even if they find later this term that there is a way to gauge extreme partisan gerrymandering.

"Put simply, there is no need to hurry," said an amicus brief filed by Republican officials in Alabama, Arizona, Arkansas, Kansas, Missouri and South Carolina. They noted that the 2020 Census will require new lines to be drawn nationwide anyway.

Even with the U.S. Supreme Court's decision not to intervene, the process of redrawing the maps will be strained as a result of the tight elections timeline and the highly polarized politics surrounding the matter.

The Pennsylvania high court wants the legislature to submit a new plan to the governor by the end of this week and said the governor should have it ready for the state court's review by Feb. 15.

Pennsylvania's governor, Democrat Tom Wolf, indicated that was possible.

"Gerrymandering is wrong and we must correct errors of the past with the existing map," he said in a statement. "My team is ready, willing and able to work with the General Assembly to ensure a new map is fair and within the clear orders given by the Pennsylvania Supreme Court."

But Republican leaders have taken no action to draw new maps and have filed another request for delay at the state Supreme Court. They have questioned whether two of the Democratic justices should be disqualified from the case because of comments they made about gerrymandering during the elections.

And a Republican justice, after questioning, filed a disclosure noting that she had accepted $25,000 in campaign contributions from a fund controlled by Senate President Pro Tempore Joseph B. Scarnati (R), one of the legislative leaders who brought the case.

Pennsylvania is scheduled to hold congressional primaries May 15. Because the district lines are in question, filing for the races has been pushed back to March 20.

In their appeal to the U.S. Supreme Court, Pennsylvania's Republican legislative leaders said that, just as when the court decided to reverse the Florida Supreme Court's decision in Bush v. Gore, there is a federal issue at stake.

The U.S. Constitution's elections clause provides that the "Times, Places and Manner" of congressional elections shall be decided by the "legislature" of each state, or by Congress. That leaves no room for the Pennsylvania Supreme Court to usurp the legislature's power under vague interpretations of the state's guarantees of free speech and equal protection, the state Republicans say.

The Pennsylvania court's 5-to-2 ruling was not accompanied by a detailed opinion; it said one would come later.

"For the first time in United States history, a state court, in attempting to play the role of 'lawmaker,' has invalidated a congressional districting plan without identifying a violation of the U.S. Constitution or a state constitutional or statutory provision providing specific redistricting criteria," the GOP leaders told the court.

But the League of Women Voters of Pennsylvania, one of the challengers to the plan, told the U.S. Supreme Court in its response brief that the justices on numerous occasions have said the meaning of "legislature" in the Constitution is not so literal.

To rule for the commonwealth's legislative leaders, "this Court would need to overrule no fewer than six of its precedents, all upholding the power of state courts to review and remedy unconstitutional congressional districting plans," the group's brief said.

It added, "Their stay applications are just a ploy to preserve a congressional map that violates Pennsylvania's Constitution for one more election cycle."