Originally Posted by
joshwex90
I've never transited IAD, so I don't know if they have a different set-up. But in general, when flying to the USA, you must claim your bags at the first port of entry (even if not leaving the airport and connecting to an international destination,) and then re-check
It is the same at every US airport: you must claim your luggage at the first port of entry into the US in order to clear customs (except in those airports in Ireland, Canada, Abu Dhabi, and the Caribbean where US immigration and customs is pre-cleared before you board your international flight).