Probably from the RNC mailing list handed over to the DNC by 'Rainman' Boehner and the rest of the scurvy GOP-e brain trust.
Geeez. I think the DNC has spent a lot of money buying the list of registered voters, because it’s addressed to me, exactly as I’m registered. Here in my state, we’re not registered by party.
Even includes pre-paid postage return envelope which I will use, of course.