JF,  I respectfully disagree.  Theodore Roosevelt made the same type of promise, not to run for president after his second term.  Like Bernie, he would have been easily forgiven by his supporters and all who wanted to move this country forward would have breathed a sigh of relief.  Occasionally, men and women of principle have to override their personal principles for the common good.  After four years of Taft, TR couldn't take it anymore and formed the Progressive Party which had an enormous influence on that other party renegade, Franklin D. Roosevelt.  FDR eventually carried on TR's "Square Deal" with the "New Deal".