US operates out of Terminals B and C at DCA, and DL is in Terminals A and B. If you can get US boarding pass either with OLCI or in ATL and if both of your flights are in Terminal B you'll be fine unless your first leg is delayed by more than about 35minutes. If you're going between B and C there is a trolley/shuttle bus; I have only taken it the other way, from C to B but I believe it goes in both directions (can't imagine why it wouldn't) and you'd probably be fine unless your first leg is more than 20-25 minutes late. It's about a 2 or 3 minute ride and you never leave the sterile area so no trip through security.

If you're going between A and C or A and B it would be iffy at best, no people mover, fastest way to get between the two is leave the airport, wait outside for the shuttle bus, arrive at B/C and clear security again. Security at DCA is very hit-or-miss, especially in Terminal C. Most of the time I sail through in under 5 minutes; lines move quickly. But when it's backed up, it's a nightmare. I've spent upwards of 45 minutes in that line.

Your TA can probably tell you which terminals your flights are in. Most of the US stuff is in C but I actually think ALB flights may originate from B.

As for your BP, there are all sorts of business traveller resources in ATL; I bet there is somewhere you could do your OLCI and print your US BP right in that airport. If not, and your "few hours" is enough hours, take a cab to whatever FedEx/Kinkos is closest to the airport, ask it to wait while you go inside and print out the BP on their computer, and head back to the airport.

I would NOT count on the luggage making it, though; it regularly takes upwards of 20 minutes for bags to be unloaded from inbound flights at DCA.