text:  Well, there are no precedents what Joe Biden has done by withdrawing from the presidential race because he's done it at such a late stage. In 1968, when Lyndon Johnson, who was then president, stepped aside, in large part because of America's disastrous intervention in the Vietnam War, the primaries were still going on. So you still had a contest that was developing. There were challengers like Eugene McCarthy. Then later, Bobby Kennedy would come into the race. In this case, the primaries had already wrapped up.