No it's not. Not even close.
The stink over Obama's comment was that he was insulting a significant, though marginalized, portion of the voting population. It was "quickly forgiven" because it didn't call into question his sanity or whether or not he was pandering and, really, there was some truth to what he said. It quickly passed because it really wasn't that huge of a deal and didn't call into question his mental state.
That does not, in any logical way, compare with Cain (and Bachmann, per Rugrat's link) claiming that he was given a directive from an invisible being (whose existence is questionable, at best) to run for the most powerful position in the world.
No matter how you try to rhetorically twist the facts into an argument pretzel, the two are not in any way logically connected.