The question will be asked, a reasonable and electorally viable answer will be given - and the birthers will have a cow and decry the GOP nominee as a betrayer of the Constitution.
They couldn't possibly be much MORE marginalized, so what do they have to lose?
Oh yes they can. At the moment sites like this one and others allow birthers to post (though sometimes restrict how many threads they can start), radio hosts like Levin, Beck and Hannity mostly just ignore them, politicians generally just don't comment on their claims, Fox News just doesn't cover them, etc. In short, birther conspiracies are generally ignored and those pushing them are sort of tolerated as long as they don't make a giant nuisance of themselves. The minute they become a serious detriment to the conservative cause by rejecting our nominee or making us all look batty in the middle of a campaign season, conservatives will go from ignoring them to attacking them. Once that happens it will wipe out any remaining sympathy they might have had in some conservative quarters which will decimate their ranks and leave only the truly hard core fringe fanatics - which we can safely ignore as their numbers will be so tiny as to be meaningless. Birthers get mad at hosts like Levin for hanging up on the now, just wait if they actually start threatening to vote against our eventual nominee for rejecting their birther agenda - hosts like Levin will go from ignoring them to outright condemning them.