If Democrats were sly, there is a way out. The Baptist southern presidential candidate should start a campaign to get the goddamn Federal government out of the marriage business. It has to be framed that way. Marriage should be a faith-based institution and we should turn it over to the churches. If someone doesn’t want to be married in a church, then the Federal government can offer them a legal civil contract (this is a better name for it than civil union). That’s not a marriage and the candidate could solemnly observe that they are taking their salvation in their own hands if they go that route, but that is their business. But marriage is sacred and the churches should be in charge of it.
If you succeeded in getting the Federal government out of the marriage business, then the whole issue would collapse on the Republicans. You appeal to populist sentiments against the Feds and to the long Baptist tradition of support for the US first amendment enshrining separation of religion and state.