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And, as he points out, once the other candidate has endorsed the presumptive nominee, this doesn't happen.
It would be one thing if neither candidate actually had enough delegates for the nomination and one hadn't endorsed the other. Then, go to the convention and fight it out. But, barring someone finding out Obama is actually a space alien (which might be a solution, we've never had a space alien - that we know of - as a President before, although Jerry Brown did run as Governor Moonbeam) he's the nominee.
I say this as someone who was not a supporter of either candidate, who wasn't particularly bothered by the actual political stuff in the primaries, or fact that it went to the end of the primary season (as opposed, btw, to the press coverage, which gets worse every election) - there is no point to this. If these people aren't going to vote for Obama, don't vote for him in November. If they feel that there are some issues where he does not represent them, find a way to make their voice heard at the convention and impact the platform. But this serves no useful purpose.