It's called Erickson Hypnosis

The use of Ericksnian “vagueness” in speech as a linguistic induction tool: “Change” and “Yes we can.” When Obama says “change” is can mean a lot of different things to everyone. He is not specific in what he means because then he would lose his pacing of the audience.
Obama speaks for 40-50 minutes, 20-30 minute longer than most political speeches. Have you ever wondered why Obama gives these long 40-50 minute speeches? Probably not, because most people do not even realize time has gone by. This process of pacing then leading, pacing then leading, again and again, as well as using other hypnotic language patterns is called “stacking language patterns” (as in, one on top of the other)
The hypnotist blends the process with embedded commands, anchors, emotional transfers, and other techniques. What occurs is that the critical factor is bored, worn down, gets tired, and stops being critical because it is too much work – then, the hypnotist’s effects increase.

“a light will shine down from somewhere, it will light upon you, you will experience an epiphany, and you will say to yourself, “I have to vote for Barack" as he secures this suggestion with hand signals aimed at you. By the way, Obama actually said this in a speech.
Read the full article .. it makes a lot of sense ..