The Democrat-led Illinois Supreme Court on Wednesday said Republicans waited too long to contest the 2021 redrawing of legislative districts that has maintained Democratic majorities in the state House and Senate.

Republicans had argued the Democratic mapping effort was unconstitutional political gerrymandering that limited voters’ choices. But the court’s five-member Democratic majority said the GOP’s “timing in filing the instant motion shows a lack of due diligence.”

“Plaintiffs could have brought their argument years ago,” the majority wrote in an unsigned decision. “Their claim that waiting multiple election cycles is necessary to reveal the effects of redistricting is unpersuasive.”

Of the court’s two Republicans, Justice David Overstreet dissented from the majority and Justice Lisa Holder White took no part in the case.

At issue was a Jan. 28 Republican challenge to the redrawing of legislative districts by Democrats who control the General Assembly that occurred following the 2020 federal census.

Led by House Republican leader Tony McCombie of Savanna, the GOP contended the political gerrymandering of maps violated a state constitutional requirement that districts be “compact” and that elections be “free and equal.” In making the argument, the GOP said the boundaries limited voter choice.

In their lawsuit, Republicans contended that under a 1981 standard adopted by the Illinois Supreme Court involving a single district’s boundaries, 52 of the 118 Illinois House district boundaries violate being constitutionally compact.

The 2021 legislative redistricting map, used in elections in 2022 and last November, has resulted in Democrats gaining and maintaining a 78-40 supermajority over Republicans in the state House and a 40-19 advantage in the state Senate.

House Republicans had sought to use the results of those two elections to bolster their case, citing as guidance a U.S. Supreme Court decision on redistricting. But the state’s high court majority said the decision to wait more than three years after the maps were signed into law by Democratic Gov. JB Pritzker failed to recognize “the expeditious filing and disposition of every previous redistricting case considered by this court since the adoption of the 1970 (Illinois) Constitution.”

In reaching their finding, the court majority did not address the House Republicans’ gerrymandering claims. Instead, in allowing Democratic legislative leaders House Speaker Emanuel “Chris” Welch and Senate President Don Harmon to intervene in the case, majority justices accepted their argument and introduced the legal timeliness doctrine of “laches” to redistricting challenges — though the state constitution contains no specific time limit for filing such an action.

Generally, under the “laches” doctrine, the majority of justices said Republicans knew or should have known of their claim but unjustifiably delayed asserting it, and that the delay would negatively hurt the Democratic defendants.

Republicans’ “approach would also be prejudicial and create uncertainty for voters and officeholders alike, now and in the future, as to whether any redistricting plan in Illinois is ever final,” the court majority wrote. “We are now closer to the next decennial census than the last.”

Under a 2019 U.S. Supreme Court ruling, the issue of partisan political gerrymandering is not subject to federal court review and is left to the states. Under the state Constitution, the Illinois Supreme Court has sole jurisdiction over redistricting cases.

House Republicans assailed the ruling as political “dirty work” by Democratic justices to uphold Democrats’ legislative power and vowed to seek ethical reforms for the state’s highest court.

“Never has a greater injustice been foisted on the voters of Illinois through a judicial decision than it was today. Two hundred seven years of our state’s history and this has to be the absolute worst,” said state Rep. Dan Ugaste of St. Charles, a member of the House GOP leadership.

“They had the chance to make this right, just to give the voters a chance to pick their representatives instead of representatives picking their voters, and they declined. And why did they decline? Because of a technical term in the law that I believe was completely misapplied,” he said. “Someone has to be called to account on this.”

In his dissent, Overstreet noted the U.S. Supreme Court’s ruling that political gerrymandering was not justiciable in the federal courts. He said that while the state’s highest court in the past has indicated ‘“political fairness’ is an Illinois constitutional requirement for redistricting plans, it has yet to provide standards and guidance” for what that entails and how it should be enforced.

Overstreet also disagreed with applying the “laches” timeliness standard to the case.

Chicago Tribune’s Jeremy Gorner contributed.