(Reuters) - The U.S. Supreme Court’s ruling that federal judges have no power to police partisan gerrymandering - the practice of manipulating electoral district boundaries for political gain - likely will embolden politicians to pursue more extreme efforts free from the fear of judicial interference, experts said.

FILE PHOTO: A girls colors an electoral map of the United States in either red or blue in Raleigh, North Carolina, U.S. November 8, 2016. REUTERS/Jonathan Drake/File Photo

“We’ll see more states doing more bad stuff,” said University of California at Irvine election law expert Rick Hasen.

The court’s 5-4 decision on Thursday, powered by its conservative majority in a ruling authored by Chief Justice John Roberts, to close federal courthouse doors to partisan gerrymandering legal challenges shifts the focus of countering electoral map bias to the states.

Election reformers now face a limited menu of options, all of which face potential obstacles: voter ballot initiatives, lawsuits filed in state courts and congressional legislation.

“The hope from the reform groups was that you would just be able to wave a wand over the entire country and fix all the gerrymanders,” said Michael McDonald, a University of Florida expert on U.S. elections. “Roberts said the battle that was in the states will stay in the states.”

The geographical boundaries of U.S. House of Representatives and state legislative districts across the country are redrawn to reflect population changes measured by the census conducted by the federal government each decade. The next census is in 2020. In most states, redistricting is done by the party in power.

Gerrymandering is carried out by configuring districts in a way that packs as many like-minded voters as possible into a small number of districts and distributing the rest in other districts too thinly to form a majority.

President Donald Trump’s fellow Republicans have been the primary beneficiaries of gerrymandering since the last round of redistricting following the 2010 census, though Democrats have engaged in the practice as well. Hasen said he expects more Democratic-led legislatures to engage in the practice in light of the ruling.

“I think there will be a lot of pressure on Democrats who may have held back to do so, because this has national implications,” Hasen said.

The court ruled in cases from North Carolina and Maryland. In addition to ensuring that voters from those states will cast ballots in the 2020 election under the same electoral maps that were challenged, Thursday’s ruling also hurts plaintiffs in Ohio, Michigan and Wisconsin who have sued in federal courts, saying their voting power had been curtailed by gerrymandering.

In the longer run, countering gerrymandering will fall back to state legislatures, courts and voters themselves. Outside groups are drawing battle lines.

“We’ll continue to fight against map manipulation using every tool that is at our disposal,” said former U.S. Attorney General Eric Holder, whose National Democratic Redistricting Committee is backed by former President Barack Obama, a Democrat, and former California Governor Arnold Schwarzenegger, a Republican. “But even without no federal guardrail on gerrymandering, this fight is far from over.”

The National Republican Redistricting Trust said it would oppose any effort to take away legislators’ authority.

“This is not the end of our fight,” former Wisconsin Republican Governor Scott Walker, the group’s fundraising chairman, said in a statement. “The battle to protect our country from Barack Obama and Eric Holder’s plan to hijack our elections now moves to the states.”

In recent years, voters in several states, including Colorado and Michigan, have approved ballot measures creating independent commissions to handle the post-census process of redrawing electoral districts. About a quarter of U.S. states have given a commission either full or partial authority in redistricting.

Efforts already are underway in several states, including Arkansas, Nebraska and Oklahoma, to launch similar ballot initiatives next year.

Election law expert Nicholas Stephanopoulos, a University of Chicago law professor, said only about half of states allow ballot initiatives.

Reformers also could file challenges to gerrymandered maps in state courts, whose authority under state law is unaffected by the Supreme Court’s decision.

NORTH CAROLINA BATTLE

Next month, a North Carolina court will hold a trial in a case brought by advocates who claim Republican-drawn districts violate the state constitution, a dispute likely to be resolved by the state’s top court. Nine of the state’s 13 U.S. House seats are currently held by Republicans, even though Democrats lost the total statewide vote last year by only 2%. A new election has been called for one seat because of election fraud.

Legal experts have said the state’s high court, which has six Democrats among its seven justices, could follow in the footsteps of Pennsylvania’s Supreme Court, which in 2018 threw out a Republican-created map and commissioned an independent expert to draw new lines. Democrats there won half of the state’s 18 House seats in 2018, after holding only five seats under the old map.

Many state constitutions include language on fair elections or free speech that goes beyond the U.S. Constitution, potentially opening a legal path for gerrymandering opponents.

Meanwhile, many states with severely gerrymandered districts have legislatures and courts dominated by the same party, making it unlikely that judges would take action. In Texas, Wisconsin and Florida, Republicans dominate both the legislature and the top courts, while Democrats do the same in Illinois.

“There’s no hope for reform in some of the states with the worst gerrymandering,” Stephanopoulos said.

A solution in the U.S. Congress appears unlikely. The Democratic-led House of Representatives passed a sweeping voting reform bill this year, including a nationwide ban on partisan gerrymandering, but the legislation has no chance of approval in the Republican-controlled U.S. Senate.

Election law expert Michael Li, an attorney at the Brennan Center for Justice at New York University Law School, expressed optimism, in part because of the increased public awareness of the issue.

“There’s a lot more sunshine on the process,” Li said. “It doesn’t mean you’ll win every time, but it means you’ll have a fight.”