Nixon, LBJ and Truman had some training as former VPs. In Nixon’s case, a full eight years. In Truman’s case, a mere few months.
LBJ was the quintessential senator and the force in the senate at the time of his vice presidency.
Nixon actually had a functional presidency until the Watergate takedown. Billy Graham reveals that Nixon had a level of anti-Semitism in him, and that bothers me now. Also, after becoming a conservative, I’ve decided that Nixon, with his wage/price controls, was actually a bit of a socialist.