He opposed the partial-birth abortion ban, because it might strengthen his fictitious bogeyman, the "religious right." (Homosexuals feeling good apparently trumps saving babies from getting their brains sucked out). He also sided with Sen. Charles Schumer when Schumer wanted to use 9/11 as an excuse for making a permanent database of gun sales. He flirted with supporting Howard Dean until it became obvious Dean was tanking--this when Bush had not supported the marriage yet. He at one point attacked Newt Gingrich on some national security issue (I forget which one, but I think it was Taiwan), not because of the substance of Newt's generally correct remarks, but because Newt was the "most reviled American politician in recent history." (Note that Newt doesn't have a history of being especially anti-homosexual; Andrew simply doesn't like him because his homo friends tell him not to like him). He rejoiced at the departure of Phil Gramm, not because Gramm was any kind of an extremist--he admitted he wasn't--but because he had a Southern accent and therefore was beyond the pale.
The really ironic thing here is that Sullivan has gloated about the triumph of "gay" culture--even to the point of saying, not without some validity, that it's now the dominant culture--yet now that Bush supports the FMA, he acts as if homos were some beknighted victims. He can't have it both ways: they can't be persecuted dictators.
I think part of his rage is that Bush stole his show: he was planning on back-stabbing Bush in late October, and instead Bush has forced his hand now. No one is running headlines of "Sullivan endorses Kerry" at a crucial time; instead they're saying "Bush endorses gay marriage ban." As usual, Sullivan is angry at being the first one kicked to the curb.