"Not surprising, Boren jumped the shark around 1994."
Do you have any specifics?
That's when he suddenly left the US Senate, with a couple of years left on his term, to become the head of the University of Oklahoma. Very few politicians, especially Democrats, give up the kind of power a Senator has, unless to run for another office, and usually not even then. It's virtually unheard of for them to do so 2 years before their term expires.
As a counter example, Bob Kerry decided not to run for reelection to the US Senate from Nebraska, even though he was pretty sure to win if he had, to become President of the New School University in New York City, but he did so at the end of his second term as a Senator.