The partisan differences aren't even especially large in most places. There are plenty of places deemed a "deep red district" or "deep blue district" where the typical outcomes are 60-40% or so (like CA-4, the "deep red" central valley district). The difference between a "deep red" 60-40% district and a 50-50 swing district is 1 out of 10 people having different opinions. For prognostication purposes these are considered solid districts for one party or the other, because it's hard to flip 1 out of 10 people in a single election. But in terms of what it's like to live in one or another, it's not a huge difference in who your neighbors are.