You know, I don't even know how to answer this.
So I don't know why I'm replying, but here goes:
I don't think that Bush would plot to have Obama assassinated. First, I don't think he could do it, temperamentally. Obama is part of the fraternity of public servants. You don't take a contract out on one of your brothers, even if you don't like him. Second, it sets a very bad precedent. Presidents don't have each other knocked off, not in this country.
It would be better for Obama to fail than to die.
Even if there were some crazy plot coming from a loon in the Bush Administration, or the Republican Party, the Secret Service is made up of professionals who serve the nation. They aren't the damn Praetorian Guard.