Blacks may be part of the explanation, though Baltimore City was more pro-gay than PG. This also was the case in the state legislative vote. I would have thought that more well-off blacks in PG would have been more pro-gay.
IIRC, Alcon (or another Wash. poster) posted Wash's results by CD, though I can't find it.
Here ya go:
https://wei.sos.wa.gov/agency/osos/en/press_and_research/PreviousElections/2012/General-Election/Data/Documents/Congressional,%20Legislative%20Breakdowns/FINAL%202012Gen%20-%20Cong.pdf
