A thirty or sixty-second message to a largely uninterested audience is not a good opportunity for a lecture. Points of personal history, position, or policy are more likely to bore than persuade. But politicians usually can’t resist talking about themselves and what they think. They, of course, find the subject engrossing and find it hard to believe that others won’t.
From a TV ad, viewers don’t want an education. They are looking for an experience.
The most important thing any politician needs to get across is what it would feel like to vote for them. Issues, upbringing, friends, enemies, accomplishments, promises—all are colors in the palette that can be used to evoke what a vote would feel like.
In this ad, Sanders tells us nothing of his personal history or his points or view. We only learn the reaction many others have had to him. Those visuals, together with the Simon and Garfunkel track, communicate the wild enthusiasm of supporters who seem to sense a genuine, unselfish break with the establishment and the possibility that it could happen.
The point here is not to argue feasibility or electability. Those discussions are for other times and places. The point here is to give potential voters a sample how it would feel to support Sanders. It works.