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.

After the governor – now a Democrat – and the still-Republican state legislature deadlocked on a new map, the state Supreme Court drew one that made districts in the state far more compact and contiguous.

The new map, which now almost certainly will be the lines under which candidates will run in 2018, also handed Democrats a series of opportunities including at least three seats in southeastern Pennsylvania and several more improved opportunities in places like Allentown and southwestern Pennsylvania.

(For much more on the map fight, check out my Q&A with the Philly Enquirer’s Jonathan Tamari.)

For Democrats, the Supreme Court order is good news on top of good news. The national political environment – as signaled by Lamb’s likely victory in a district that Trump won by 20 points in 2016 – suggests that a large-ish Democratic wave is building in advance of November. Trump’s unpopularity, historic trends against the party in power in midterms and the tremendous energy within the Democratic base (again, thanks to Trump) are creating a political climate where Republicans who never thought they would have to worry about a challenge in the general election now have to start worrying.

Onto all of that lands this ruling in Pennsylvania, which, according to neutral observers is likely to net Democrats three seats minimum this fall. If, say, Democrats could raise that to five seats, then more than 20% of all the seats they need to pick up to retake the majority might come from Pennsylvania alone.

Then there is the broader import of the Supreme Court declining to hear the redistricting appeal by Pennsylvania Republicans. Pennsylvania is one of a handful of states with ongoing battles over how much partisanship and politics is too much partisanship and politics when it comes to redistricting.

The Court is currently considering redistricting cases in Wisconsin and Maryland – the first was brought by Democrats, the second by Republicans – that deal with this same topic, but are in federal court as opposed to state court.

The broader point here is two-fold: 1) This is a major win for Democrats hoping to retake the House majority this November and 2) If the Court ultimately decides that extreme partisan gerrymandering is unconstitutional, it will have a profound effect on how maps gets drawn – and who controls the House majority – in 2021 and beyond.