Bellwether regions of the U.S. house?

[Tekken_Guy]

What parts of the U.S. have constantly been represented by the party in the house majority?

[Thank you for being a friend...]

Pennsylvania's Main Line, the suburban counties outside Philadelphia
The Lehigh Valley (Allentown, Bethlehem, Easton)

There seems to be a few seats in Upstate New York that flip.

A few Indiana districts used to be very competitive, but that's not as much the case at present.

Honestly, it's changed so much since 1994 for Republicans and 2006 for Democrats.

[Calthrina950]

Maine and New Hampshire seem to have bellwether or swing districts that have oscillated between the two parties for decades. This was also true of Connecticut until the 2000s.

[Gracile]

NH-01 has been a good recent bellwether for House control, as well as closeness to the national House vote margin. Since 2006, it has voted for the party that controlled the House in all but two cycles - 2012 and 2016, and even in those two elections they were close to the House NPV (D +3.1 NPV and D +1.1 in NH-01 / R +1.1 NPV and D +1.3 in NH-01 for 2012 and 2016, respectively).

[Joseph Cao]

Sabato's Crystal Ball tackled this question back in 2018, looking strictly at which regions have been represented by the majority party for the longest unbroken period.

TL;DR, as of the time that article was published, a patch of eastern Ohio was consistently in this category since 1954 but that streak has since been snapped. Currently the best that can be done is 1994, and several areas fall into this category:

- Bits of Lackawanna, Pike, and Wayne counties in NEPA that are currently represented by Matt Cartwright, having been put into his district in the 2018 remap from where they were previously represented by Don Sherwood, Chris Carney, and Tom Marino;
- a bit of the current PA-06 that was also brought over from Ryan Costello's old district;
- the entirety of Columbia, Greene, and Otsego plus most of Delaware, Dutchess, and Rensselaer counties, previously represented by Kirsten Gillibrand and Mike Arcuri before being added to the current NY-19.

[Schiff for Senate]

New Hampshire's 1st is a very interesting  example, though now it's slightly Democratic-leaning. Presidentially speaking, it voted for Obama in 2012 by 1.7%, then went for Trump in 2016 by 1.6%. Like the rest of the state it swung hard for Joe Biden, voting for him by a solid 6%. It's NH's slightly more suburban and smaller district, in Southeast NH. Congressionally speaking - it was highly competitive but is now, again, slightly blue leaning.

 Carol Shea-Porter defeated two-term GOP incumbent Jeb Bradley in 2006 (by 2.63%), and won reelection in 2008 by 5.89% in a rematch. In 2010, admist the the GOP gaining back the House in a wave year, Shea-Porter lost her reelection bid to Republican Frank Guinta, by 11.62%. But in 2012, a less extreme year in which the Democrats recovered a handful of seats, Shea-Porter recovered her seat in a rematch of the 2010 race, winning by 1.7%. In 2014, a Democratic president's 6-year midterm, another wave ensued, and the beaten Guinta was swept in, defeating Shea-Porter by a decent 3.6%. Come 2016, Shea-Porter (in a rematch of 2010, 2012 and 2014), again picked up her seat as the Democrats saw a net gain of six seats: Shea-Porter won by a margin of 1.4%. In 2018 Shea-Porter retired and was replaced by Democrat Chris Pappas, who won by a solid 8.6%. In 2020, Pappas became the first representative of the district to win reelection since his predecessor in 2008, winning by a nice 5.1%.

 It is slightly Democratic-tilted at this point, but it was very interesting how Shea-Porter defeated a two-term GOP incumbent in 2006, lost herself after two terms (in 2010), won in a rematch in 2012, lost in a rematch in 2014 and won again in a 2016 rematch before finally retiring. It's almost like the voters of NH-01 wanted to show the country that their district was the most politically unpredictable.

[Non Swing Voter]

States where there is a lot of flipping from election to election particularly when the house flips.

For instance, California had a lot of flips from D to R last time but the house didn't flip.  Conversely Iowa had several flips and the house didn't flip.

On the other hand, the year the house flipped last a bunch of seats flipped in Michigan, Pennsylvania, Virginia, Minnesota (both ways).  So I'd say the bellwether region straddles the mid-Atlantic to the industrial midwest. 

If there weren't out of control gerrymandering the bellwether would more likely be suburban districts outside (or including) midsize cities.  Without gerrymandering, the house map should be more favorable to Dems than either the Presidential or Senate maps.  But because there's a Republican gerrymander it's more on par with the electoral college, though still easier for Dems than the Senate.  It's really appalling how all three are skewed somewhat towards Republicans right now.  Though it's not totally surprising given that the whole system was designed to slow down change.

[Young Conservative]

Strong case to be made for VA-02 nowadays.