Ridicule is a very powerful tool of the left.
Did "birtherism" doom the (R)'s election outcome in 2010?
Fact or opinion? Links please
I have a better theory. The RNC Northeastern RHINO Rockefeller Republican types made a decision early in 2008 that it would be so gauche to challenge Obama's eligibility because they felt minority voters would regard it as a dirty trick, and so to feel good about themselves, they insisted that the issue not be brought up.
As luck should have it, John McCain was the chosen Republican candidate (before anyone knew he wasn't born in the United States Proper) and so their (the RNC RHINOS) blacklisting of this idea dovetailed nicely with the proclivities of the chosen candidate anyway.
I believe a lot of RNC types worked to actively spike discussions on this particular subject because they felt it was politically troublesome.