Several races in the area are shaping up as among the most competitive in the country. Here is an early rundown of the key contests and candidates in the mix for 2018, when for the first time a national electorate will weigh in on the Trump administration:
New Jersey 2d Congressional District (based in Atlantic County)
Republican Frank LoBiondo's retirement Tuesday suddenly turned this district from an afterthought into one of Democrats' best pick-up opportunities.
The district, which roams across South Jersey from the Shore to the Delaware River, backed Trump last year, but also went for Barack Obama twice.
Democratic state Sen. Jeff Van Drew, long rumored to covet the seat, is interested in running and already has the backing of South Jersey political power George Norcross. Two other Democrats, Tanzie Youngblood and Sean Thom, are already in the race.The Republican field is still taking shape, though Assemblyman Chris Brown has been mentioned as one potential candidate.
Pennsylvania 6th (based in Chester County)
This could be the toughest race in Pennsylvania, according to insiders in both parties.
Despite the district's Republican lean, Hillary Clinton narrowly won it, a sign that some moderates and Republicans there were repelled by Trump, and presenting danger for the GOP incumbent, Ryan Costello. Democrats won row offices in Chester County Tuesday for the first time in more than 200 years.
Democrat Chrissy Houlahan is one of her party's top recruits and has the backing of an influential women's group, EMILY's List. Operatives in both parties consider her the strongest challenger in the region. Republicans are already attacking her business record, trying to bruise Houlahan early.
Chrissy Houlahan, Democratic challenger in Pennsylvania's 6th District
Pennsylvania 7th (based in Delaware County)
Rep. Pat Meehan, a Republican now in his fourth term, has built a substantial campaign fund — it had nearly $2.5 million as of Sept. 30. In a district that snakes through five counties, it can be hard for challengers to get their names out.
As in the sixth, however, Democrats hope to seize on Clinton's victory there last year. They also stormed to historic victories in county races Tuesday.
First they have to sort out a crowded primary featuring at least five candidates. The most well-known is state Sen. Daylin Leach, who boasts name recognition and fund-raising ability. But some Democrats worry that the outspoken liberal may win the primary but prove out of step with the moderate district.
Pennsylvania 8th (based in Bucks County)
Democrats have returned to a theme they've tried here before, recruiting a veteran to challenge in a district that Trump narrowly won.
Rachel Reddick, a former Navy Judge Advocate General, has the inside track to take on Rep. Brian Fitzpatrick. Although the congressman is a freshman, he's running on a strong family name — his brother Michael represented the district for four terms.
Fitzpatrick has at least one primary challenger, Valerie Mihalek, who once worked in his brother's Congressional office. Dean Malik, a lawyer who has talked up his intentions several times without ever mounting a serious campaign, has said he will run, attacking Fitzpatrick for not supporting Trump strongly enough. Malik, however, has yet to file papers to make his candidacy official, according to federal records.
Democrats also scored wins here Tuesday, taking row offices for the first time in 30 years.
New Jersey 3d (based in Burlington County)
Liberal voters are up in arms in this South Jersey district, determined to take out Rep. Tom MacArthur after the Republican personally helped revive the House GOP's push to repeal and replace the Affordable Care Act.
But the district has a Trump lean. He won it with 51 percent of the vote, after it twice went for Obama, and it's hugely expensive, running into both the New York and Philadelphia media markets. MacArthur, a former insurance industry executive, has deep pockets.
Democratic leaders are lining up behind Andy Kim, a former Obama national security adviser who aided Gens. David Petraeus and Gen. John Allen in Afghanistan.
Pennsylvania 15th (based in Lehigh County) and 16th (based in Lancaster County)
Republican Rep. Charlie Dent's retirement opened up a moderate seat in the 15th district, and national Democrats are enthusiastic about Christina Hartman, who is running for a second consecutive cycle in the 16th district against Republican Rep. Lloyd Smucker. Both races are longer shots for Democrats, however. If they win either, it would probably mean they've generated a massive wave.
Sen. Bob Casey, a Democrat, is seeking his third term with a very different profile. The soft-spoken senator, long known as a moderate, has become a strident Trump critic — despite seeing Pennsylvania support the president last year.
He appears to be trying to rally a Democratic base eager to take on Trump, while Republicans say he's strayed from his Scranton roots and is too liberal for Pennsylvania.
The GOP has a crowded primary, with most party insiders expected to line up with Rep. Lou Barletta, a Northeast Pennsylvanian who has strongly embraced Trump.