Originally Posted by
pinkcat
... Was stood in the queue for 3 hours once, the mobile lounges kept dropping more and more people into the hall, the queue wasnt going anywhere and when you get towards the front you can see airport employees literally throwing your luggage off the carousel and then kicking it into place where it sits unsupervised until you finall make it through the bottleneck
These kinds of anecdotes are the reason one needs to take everything they read here with a grain of salt.
Unlike
pinkcat you will not be riding a moon buggy over too the main Arrivals terminal because you'll be clearing customs midfield (under the C terminal) before your connecting flight. While you may then ride a moon buggy over to the A terminal, it won't lead to the traumatic experience described above. Assuming you carry an American passport, immigration usually does not take 3 hours. I have passed through IAD immigration dozens of times and it has never taken me over 1/2 hour.
Absent unpredictable problems, 2 hours may be close, particularly if you check luggage, but I think it can be done.