See it's like this. Hillary wants the White House, so after losing in the primary she goes out of her way to appear supportive of Obama, even though he doesn't pick her for V.P. She gets cozy with Biden, who hates Obama. Biden goes out of his way to appear foolish (not a stretch), so Obama doesn't object to Biden dropping out. Biden suggests Hillary as a replacement. Hillary of course seems like the logical replacement. The Obama/Clinton ticket wins the election with a huge majority. Hillary, however is not content to play second fiddle to Mr. Funnyname. She will then secretly leak information about Obama so horrible it will get him impeached. Voila, President Clinton.
By the way I don't believe this at all. Just felt like a good conspiracy theory.