(CNN) On Monday afternoon, the Supreme Court handed Democrats a major victory in the party's attempt to retake the House this November, turning aside an appeal by Pennsylvania Republicans that would have kept the state's new congressional map from being in effect for the coming primary and general elections in the Keystone State.

"For Democrats, it means a likely pickup of additional 4-5 seats," said Marc Elias, a noted Democratic elections lawyer. "Democrats only need 23 to retake the majority in the House, so this is one big chunk."

At issue was a map put in place by Republicans at the state level in Pennsylvania following the 2010 census.

Despite the state's demonstrated Democratic lean (President Donald Trump was the first Republican to carry the state at the presidential level since George H.W. Bush in 1988), the map usually advantaged the GOP. Republicans currently control 12 seats. Democrats will control six, assuming that Conor Lamb's victory in the 18th district special election stands

Democrats filed suit and the state Supreme Court, where Democrats seized majority control in 2015, sided with them, ordering that the map drawn by Republicans in the state legislature and the governor's office was motivated too much by political concerns and needed to be redrawn.

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