His letter of resignation is here, and it is must-reading for every student of legal ethics and anyone who wonders whether any lawyers have principles.
Note that Paul (who has been a long-time friend) declines to state whether he, personally, agrees with DOMA. His position -- a sound one -- is that, having undertaken a representation, it is wrong for a law firm to abandon it simply because it has become unpopular and controversial in some quarters.
If there were any consistency on the left, all those who have saluted the fervent advocates of terrorist detainees would be hailing Paul as a man of principle. Don't hold your breath in anticipation, though -- you'll turn blue and die.
It's remarkable that, in a city where defending people who want to kill innocent Americans is tolerated (and even celebrated by some), representing proponents of the age-old understanding of marriage simply requires too much moral courage for King & Spalding. All its clients now must wonder if, should they become inconveniently controversial, their cases will be jettisoned by the firm, as well.
Paul will now be working at Bancroft PLLC. He is a fine lawyer (one of the nation's best) -- and also, as his behavior attests, a fine man.