She is a temptress. Her goal is to become president of the US..that's how hungry she is. She will attempt to blackmail him to choose her in a sense that she will indirectly get her supporters to vote for McCain or make Obama's life hell if he doesn't choose her.
And if she were to become VP and OBama, Gd forbid, wins, she will find a way to screw him over so that for the next elections or during his presidency he gets impeached.