IAD is a cinch as a foreign national when it comes to immigration.
The worst I ever experienced was about 25 minutes. My last three transitions were significantly less than 2 minutes and I was definitely through ahead of most citizens.
Even on the morning arrivals from South America, immigration hardly ever eats more than 15 minutes.
The HUGE bottleneck is the luggage. It
is improving somewhat but I still dread it a lot. Especially after a few flights to TPE, SIN, BKK, NRT now where the bags pop out the minute you walk to the conveyor..

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