if your flight is on time 6:30 is doable with a mobile boarding pass and TSA Pre. however, if you're late inbound on AS and you miss it, you might find the 7:30 flight to be full and putting yourself in a bad situation of having to standby, or connect in PHL/LGA to get back on track and avoid a DCA overnight.
why not book PDX-BOS nonstop on AS? already bought the DCA ticket?