HARRISBURG, Pa. (AP) — The map of congressional districts imposed by Pennsylvania's high court for the state's 2018 elections will set off a new legal battle, reconfigure perhaps dozens of campaigns and give Democrats a boost in their mission to wrest control of the U.S. House.

The map of Pennsylvania's 18 congressional districts is to be in effect for the May 15 primary and substantially overhauls a Republican-drawn congressional map widely viewed as among the nation's most gerrymandered.

The Democratic-majority state Supreme Court voted 4-3 on Monday to impose the new map it drew. New boundaries will usher in changes to Pennsylvania's predominantly Republican delegation already facing big changes in a year with six open seats, the most in decades.

Republicans vowed to immediately challenge it in federal court. Meanwhile, candidates finding themselves in a new political landscape are rethinking campaigns a week before they can start circulating petitions to run.

Most significantly, the new map gives Democrats a better shot at winning a couple more seats, particularly in Philadelphia's heavily populated and moderate suburbs. There, Republicans have held seats in bizarrely contorted districts, including one labeled "Goofy Kicking Donald Duck."

Republican Rep. Ryan Costello, whose suburban Philadelphia district was narrowly won by Democrat Hillary Clinton in 2016, is in even more dire straits now that his district adds the heavily Democratic city of Reading.

The map also removes the heart of one district from Philadelphia, where a crowd of candidates had assembled to replace the retiring Democratic Rep. Bob Brady, and moves it to suburban Montgomery County.

The new map does not apply to the March 13 special congressional election in southwestern Pennsylvania's 18th District to fill the remaining 10 months in the term of former Republican Rep. Tim Murphy, who resigned amid a scandal. But it renders the special election virtually meaningless: the court's map puts each candidate's homes in a district with a Pittsburgh-area incumbent.

The court ruled last month that Republicans who redrew district boundaries in 2011 unconstitutionally put partisan interests above neutral line-drawing criteria. It was the first time any state court threw out congressional boundaries in a partisan gerrymandering case, this one brought by registered Democratic voters and the League of Women Voters last June.

The new map repackages districts that had been stretched nearly halfway across Pennsylvania and reunifies Democratic-heavy cities that had been split by Republican map drawers six years ago.

Democrats cheered the new map.

"It remedies the outrageous gerrymander of 2011, and that's the important thing, that the gerrymander be over," said David Landau, the Democratic Party chairman of Delaware County, which was ground zero for the "Goofy Kicking Donald Duck" district. "All that zigging and zagging is all gone, and it makes Delaware County a competitive seat now."

Mark Harris, a Pittsburgh-based GOP campaign consultant, was one of many Republicans bashing the new product.

"It's a straight Democratic gerrymander by a Democratic Supreme Court to help Democrats," Harris said.

Independent analysts said the map should improve Democratic prospects while still favoring Republicans as a whole. An analysis conducted through PlanScore.org concluded the court's redrawn map eliminates "much of the partisan skew" favoring Republicans on the old Republican-drawn map, although not all of it.

University of Florida political science doctoral student Brian Amos said Clinton beat Republican Donald Trump in eight of 18 districts in the 2016 presidential election on the court's map. That compared with six of 18 districts Clinton won in 2016 under the invalidated map.

Pennsylvania has provided a crucial pillar of support for Republican control of the U.S. House.

Republicans who controlled the Legislature and the governor's office after the 2010 census crafted the now-invalidated map to elect Republicans and succeeded in that aim: Republicans won 13 of 18 seats in three straight elections even though Pennsylvania's registered Democratic voters outnumber Republicans.

Republicans will argue in federal court that legislatures and governors, not courts, have the constitutional responsibility to draw congressional maps. But they appear to face an uphill battle since federal courts are normally reluctant to undo a state court decision, said Michael Morley, a constitutional law professor at Barry University in Florida.

"I think it will be a major obstacle and a major challenge to get around it," Morley said.