Zero seconds
If I were running for President in a competent manner, I'd be well aware of the baseless, hateful rumors that have been floating out there for some time, and I certainly would have had anticipated such questions and I'd have an appropriate response ready. I sure Obama has a good response ready for such nonsense.
Of course, neither Obama nor myself would have any ulterior motive in intentionally allowing such ugly innuendos to fester within the minds of our supporters...