I think I know what blow is, but choom? Other than the myriad of recent news gossip articles about Obama and choom, I find a reference to it being a kind of hut.
Now a soon-to-be published biography by David Maraniss entitled “Barack Obama: The Story” gives more detail on Obama’s pot-smoking days, complete with testimonials from young Barry Obama’s high school buddies, a group that went by the name “the Choom Gang.” Choom was slang for smoking marijuana.