Because the martyrdom would make that of JFK look like small potatoes, if something did happen to him.
Sadly, it is better for him to limp through the next 2 years and leave as the worst president in US history.
To the guys who pull the levers of power, obama's reached the end of his usefulness. He can shuffle off at the end of his term as a failed president, taking his party down with him, or...
Cui bono?