Pennsylvania’s looming loss of a congressional seat will ripple across state politics and shape the balance of power in Washington.

The state will officially drop to 17 U.S. House seats because of sluggish population growth, the Census Bureau said Monday. Redrawing the congressional map could have massive implications for sitting lawmakers, whose districts will all grow, altering the political leanings and potentially forcing two incumbents to compete for a single seat.

The impact goes beyond Pennsylvania. Republicans need to gain just five seats to take control of the House and likely stifle President Joe Biden’s agenda. So as maps across the country are redrawn, squeezing even one seat out of Pennsylvania’s evenly split delegation could be huge.

“The national parties will be exerting a significant amount of pressure because control of the House is so narrow,” said J.J. Balaban, a Democratic strategist from Philadelphia. “The stakes are really high.”

There are many ways the redrawing could play out. But early analyses by independent experts and Pennsylvania political operatives suggest one possible scenario is that two or three conservative districts, representing areas that are losing population, may get consolidated. That might look good for Democrats at first glance — three Republican-held districts turned into two — but the ripple effects mean parts of those conservative districts would likely be added to Democratic-held swing districts.

“You could have a situation where a ... Republican seat is eliminated, but yet it’s easier for Republicans to pick up one of the remaining seats,” Balaban said.

Mark Harris, a Pittsburgh-based GOP strategist, agreed, arguing that a reasonable Republican aim would be a map that breaks up a GOP-held district but nudges rightward the competitive, Democratic-held districts in Northeastern Pennsylvania, the Lehigh Valley, and the Pittsburgh suburbs.

Here are some of the key factors to watch as lawmakers in Harrisburg start drawing a new map:

The governor, the legislature, and the court

While most of the jousting will involve Democratic Gov. Tom Wolf and the Republican legislature, members of both parties say it’s very likely to come down to the Pennsylvania Supreme Court.

“Given that the governor and the General Assembly can’t even agree on who should sit on the Public Utility Commission, the idea that they will agree to a bipartisan congressional map is far-fetched,” Balaban said.

Said Harris, “Tom Wolf has made it very clear he has little interest in working with Republicans on much of anything.”

That might suit Democrats, since the court’s Democratic majority drew a map that thrilled the party just three years ago, ruling the old one an unconstitutional gerrymander. Republicans are still fuming over that.

Heated litigation seems inevitable — and the first shot has already been fired. Democratic elections lawyer Marc Elias on Monday preemptively sued Pennsylvania in anticipation of mapmaking deadlock.

‘A cascade effect’

While the current map is a likely starting point, the loss of a seat means it’s not as easy as just tweaking boundaries — the districts need to grow by about 8% on average.

“Everyone else’s seat has to move around,” said Michael Li, a redistricting lawyer at New York University’s Brennan Center for Justice. “Losing a district basically creates a cascade effect.”

Some districts are more affected than others. Early speculation centers on the 9th, 12th, and 15th — all deeply conservative districts that sprawl across the population-shedding northern half of the state’s center.

But eliminating or merging districts means some voters will be absorbed by surrounding districts.

The swing seats

Pennsylvania’s map is relatively new, so experts predicted the new lines are unlikely to change significantly.

Many seats will remain safely Democratic or Republican. Districts in Philadelphia and its suburbs have seen population growth and won’t need to change dramatically. Other Republican-held seats in more rural areas need to grow, but are so conservative they are unlikely to become competitive.

That leaves several districts that are already closely divided and where even small tweaks can make a big difference:

Susan Wild (7th), Matt Cartwright (8th), and Dan Meuser (9th)

Operatives in both parties said the 9th, west of the Lehigh Valley and south of Scranton, is one obvious candidate to be dispersed. Partly that’s because incumbent Republican Rep. Dan Meuser is widely expected to run for governor. If he leaves the seat, there wouldn’t be a sitting House member for fellow Republicans to protect.

And while Republicans don’t want to lose a seat, they could gain it back.

Some of Meuser’s conservative district would almost certainly be added to the neighboring district held by Democratic Rep. Matt Cartwright — who is already arguably the state’s most vulnerable member. The nonpartisan Cook Political Report, which uses presidential election data to characterize political leaning, rates his district R+5 — leaning toward the GOP. (The Philadelphia district held by Rep. Dwight Evans, the most Democratic in the country, is D+41).

Cartwright’s challenge is likely to get even steeper. In almost any direction the 8th can grow, it would expand into more conservative territory.

Rep. Susan Wild could be the next most at-risk incumbent. The Democrat’s Lehigh Valley district is rated “even” by Cook. If it expands westward, it would also add more of Meuser’s constituents.

Brian Fitzpatrick (1st) and Chrissy Houlahan (6th)

There are two theoretically competitive seats in the Philadelphia suburbs, but experts in both parties say the strong incumbents are unlikely to face much trouble.

The 6th, anchored in Chester County, is rated D+5, and incumbent Democrat Chrissy Houlahan has been a strong fit for the moderate seat. GOP lawmakers might try to add more of conservative Berks or Lancaster Counties, but with Chester County’s population still growing and trending leftward, it’s unlikely this district changes much, Balaban predicted.

In the Bucks-based 1st, Brian Fitzpatrick is the only Republican still standing in the Philly suburbs. Even though his district is rated “even,” Democrats haven’t been able to lay a hand on him. It’s unlikely the district can shift enough to change that.

Conor Lamb (17th)

Rep. Conor Lamb holds a moderate district centered on the Pittsburgh suburbs, rated R+2. It could become a safer Democratic seat, or much more favorable for Republicans.

Extend the district east into Pittsburgh and it turns more blue. In that scenario, fellow Democrat Mike Doyle, who now represents Pittsburgh, might lose a piece of the city and gain some of its more conservative exurbs, but his district is already D+13. Democrats would emerge with two safe Western Pennsylvania seats, instead of one safe seat and one swing seat.

But extend the 17th north or south and the district adds Trump country.

Scott Perry (10th)

Democrats thought they could beat the deeply conservative Perry, of York County, as some of the central Pennsylvania suburbs got more liberal and his district added Harrisburg. But they failed in 2018 and 2020 and have probably missed their chance.

Almost any direction his district grows will add Republican votes.

The Senate and governor’s races

The map is also intertwined with Pennsylvania’s 2022 races for Senate and governor.

Meuser (for governor) and Lamb and Houlahan (for Senate) are all considered potential statewide candidates. Normally, the safety (or difficulty) of their new districts would inform decisions about whether to run.

But they won’t have the luxury of waiting. Anyone hoping to run statewide would likely have to launch a campaign in the next few months, and it could take until early next year to see the new districts.

If any of them do run, that could influence the map. It’s a lot easier to break up someone’s district if they’re not seeking reelection.