No. Within the next 20 years or so the Republican candidate will probably be i n support of gay marriage too, or at least civil unions.
Whoah, probably not. The GOP isn't about to stop becoming socially conservative on gay rights in 20 years.
I could easily see no future GOP presidential candidates opposing civil unions, McCain supported CU's, right? I can't really see it being a viable position to oppose basic hospital visitation rights and whatnot for gay partners.
It could depend on whether or not a bunch of states legalize gay marriage. If by2028 a majority of states (or even all states) have gay marriage it may not be politically helpfull to be strongly opposed to gay marriage. If anything the republican candidate will probably argue that it is a states rights issue, but not actively oppose gay marriage.