The 4 seats the Republicans flipped in Florida, and rather more interesting the 4 seats they flipped in New York, being the key to their taking control of the House. Why they did so well in New York is one of the stories of the election (though I'm not sure there's an obvious answer).
As someone who lives in the bluest of the flipped seats, it comes down to a few Long Island-centric reasons:
1) Regionalism. Hochul is the first governor in a century to be from Upstate New York (Buffalo, to be precise) and Zeldin, who was the Republican candidate for governor, is from as far downstate as one can go (Suffolk County). This made Hochul come off as somewhat distant to many voters in New York City and on Long Island. Since Zeldin is from Long Island, he did much better there than any Republican has in a long time, which helped to drag Republican House candidates on Long Island (as well as in Rockland) across the line. There's more on this in points #6 and #7.
2) One of Hochul's most notable initiatives has been for the state to subsidize the construction of a new stadium for the Buffalo Bills. Unsurprisingly, this has been a sticking point for New York state residents who do not live upstate on both the right and the left.
3) Until the last couple of weeks before the election, Hochul essentially ran a single-issue campaign centered around abortion. It turned out that abortion was not as big of an issue in New York as crime, particularly crime on the New York City Subway, which leads me to point #4...
4) The crime spike on the New York City Subway has been driven by random attacks. This makes it more difficult to predict where incidents may occur. I was almost attacked in the subway at Forest Hills/71st Avenue in September, and Forest Hills is traditionally one of the safest areas of the city served by the subway.
5) Minority turnout was down significantly. This hurt Democratic candidates on Long Island in particular, where there is very little in the way of a Democratic white base (except for some parts of the North Shore in Nassau, as well as the Hamptons). This was less so the case in races in the Hudson Valley (and likely the reason why NY-18 in that region did not flip to the Republicans), where there is a significant white Democratic base thanks to the region being the destination of choice for wealthy New York City residents who want to buy a country home or move out to suburbia. However, NY-17, which contains Rockland County, still flipped because of...
6) How the Jewish population voted. New York is one of the few states where Jews are a large enough share of the electorate to be a significant voting bloc. Non-Orthodox Jews are among the most Democratic ethnic groups in the United States and typically vote 80-20 Democrat. Orthodox Jews are the inverse. They tend to vote 80-20 Republican, but are geographically clustered in a few counties (primarily Rockland, Orange, Brooklyn, and to a lesser extent Queens and Nassau) and were angry at Hochul attempting to interfere in religious education (some Orthodox Jewish precincts in Brooklyn gave Zeldin over
90% of the vote). A good example of this geographic clustering is the difference between how Westchester and Nassau voted. Both are counties which were traditionally Republican until the 1990s and then swung to the Democrats. However, Westchester has continued to move to the left whereas Nassau stagnated at a 55% Democrat-45% Republican split in presidential elections for the last 20 years and has never moved that far leftwards in local elections. Jews make up a similar size of the electorate in both counties but are much more evenly split between non-Orthodox and Orthodox in Nassau, whereas Westchester's Jewish population is almost exclusively non-Orthodox. But this does not fully explain its electoral tilt, leading to point #7, which is also the final point...
7) Long-term voting trends in downstate New York are heavily shaped by population trends and people's perspectives of different suburbs. Whereas Long Island and the Hudson Valley were on much more equal footing in terms of perception back in the 1950s, the Hudson Valley has become perceived as the "better place to live" (partially thanks to being less isolated, as there are very few ways off of Long Island which do not involve travelling through New York City) and has a much larger share of domestic migration driven by high-paying corporate jobs, whereas most people who move to Long Island likely already have some sort of familial connection. Long Island is not a destination of choice as it was in the 1950s, and has become seen as the place that construction workers, police officers, and other working- and middle-class individuals live in despite the presence of some of the wealthiest suburbs in the United States (think of the Hudson Valley, especially Westchester, as Surrey and Long Island as a hybrid of Kent/Essex and you essentially get the idea). I often get the proverbial cold shoulder at grad school (Oh, you're from Long Island? I bet you lick the NYPD's boots for breakfast, lunch, and dinner!) in social situations whereas classmates of mine from Westchester and New Jersey are welcomed more openly.
