Considering that this happened nearly simultaneously with the bombings, I'm willing to bet the same person/people. Considering that both Obama and a Republican senator received them, I'm thinking that it wouldn't be a radical Republican or Democrat, but more of a "centrist" who hates everyone equally. They might still be a radical left or right-winger, but someone who's gone so far over the edge as to view both parties as equally bad or evil or too lenient or whatnot.