As with every single airport US point of entery, you will clear Immigrationa and customs and be rleased to the landside of the airport. If you have to make a connection you owill have to reclear TSA security before continuing your journey.
Plus, afer u clear customs, take the escalator in Terminal D up one level.
Go back thjrough TSA security in "D". From there you can get on the Skylink if your next flight is in A/B/C.