Kevin Drum hits on something important:

The Washington Monthly: SULLY AND BUSH

Can Kerry do for Bush and the Christian Right what Bush Sr. did for Michael Dukakis and Willie Horton: make them inextricably linked in the public's mind? Sullivan may be an extreme case, but I think he's an example of what could happen if Kerry manages to link Bush strongly with the social intolerance of the Christian Right. When you combine that with his poor performance in Iraq and his lack of dedication to small government, there are a fair number of moderate conservatives who might jump ship to Kerry or — at a minimum — at least stay home in disgust.

One of the longtime arguments of mainstream Republicans has been that the Christian Right doesn't really have much influence on the party, so there's nothing to worry about. Gay marriage, though, is an opportunity to show that that's not true. After all, if Bush is willing to amend the constitution to ban gay partnerships in order to win their votes, what might he do next?

...here's the kind of ad I see. Open with the Twin Towers smoking in the background and Jerry Falwell telling us that 9/11 was God's punishment for America being an immoral nation. Pat Robertson nods in agreement. Cut to Paul Weyrich (or someone) saying that unless Bush supports a gay marriage amendment, the Christian Right walks. Fade out and then show Bush caving in by supporting the amendment. Cut to fanatic crowds of Christian Rightists cheering and stomping. Fade to black, with an ominous voiceover that asks, "What's next?"

Republicans and the right-wing media are constantly trying to tie Democrats to their least-appealing sympathizers. This shouldn't be hard to match and exceed, since Bush & co. really are very careful to keep their radical fundamentalist right cohorts happy.

Cornering Bush into a place where he has to either disavow some of the weirder beliefs of his supporters or publicly agree with statements noxious to the mainstream is a win-win.

Of course, one will have to be careful not to attack the beliefs of ordinary, sane Christians, but I'm sure that can be managed.

(update) Commenters in Drum's thread are mixed on whether this is a smart move, and say that this should at least come from some other source than the Campaign. Could be.